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In this tutorial, you will learn what a red-black tree is. Likewise, you will discover working instances of different tasks performed on a red-black tree in C, C++, Java, and Python.
In this article, you will learn-
- 1 What is a Red-Black Tree?
- 2 How the red-black tree keeps up the property of self-balancing?
- 3 Operations on a Red-Black Tree
- 4 Left Rotate
- 5 Right Rotate
- 6 Left-Right and Right-Left Rotate
- 7 Inserting an element into a Red-Black Tree
- 8 Algorithm to insert a node
- 9 Why newly inserted nodes are consistently red in a red-black tree?
- 10 Algorithm to keep up the red-black property after insertion
- 11 Deleting an element from a Red-Black Tree
- 12 Algorithm to delete a node
- 13 Algorithm to keep up Red-Black property after deletion
- 14 Python, Java and C/C++ Examples
- 15 Red-Black Tree Applications
What is a Red-Black Tree?
Red-Black Tree is a Self-balanced binary search tree with one additional piece of storage per node: its color which can be either Red or Black.
Each node of the tree contains the attributes color, key, left pointer, right pointer, and parent(except root node).
On the off chance that a child of a node doesn’t exist, the comparing pointer property of the node contains the value NIL.
A red-Black tree is a self-balancing binary search tree in which every node contains an additional piece for indicating the color of the node, either red or black.
A red-black tree satisfies the following properties:
- Red/Black Property: Every node is colored, either red or black.
- Root Property: The root is black.
- Leaf Property: Every leaf (NIL) is black.
- Red Property: If a red node has children at that point, the children are consistently black.
- Depth Property: For every node, any straightforward way from this node to any of its descendant leaf has a similar black depth (the number of black nodes).
An illustration of a red-black tree is:
Every node has the accompanying attributes:
- color
- key
- leftChild
- rightChild
- parent (except root node)
How the red-black tree keeps up the property of self-balancing?
The red-black color is intended for balancing the tree.
The limits put on the node colors guarantee that any straightforward way from the root to a leaf isn’t more than twice the length of some other such way. It helps in keeping up the self-balancing property of the red-black tree.
Operations on a Red-Black Tree
Different tasks that can be performed on a red-black tree are:
Turning the subtrees in a Red-Black Tree
In rotation activity, the places of the nodes of a subtree are interchanged.
Rotation activity is used for keeping up the properties of a red-black tree when they are violated by different tasks like insertion and deletion.
There are two types of rotations:
Left Rotate
In the left-turn, the arrangement of the nodes on the right is changed into the arrangements on the left node.
Algorithm
- Let the underlying tree be:
2. On the off chance that y has a left subtree, allot x as the parent of the left subtree of y.
3. On the off chance that the parent of x is NULL, make y the root of the tree.
4. Else if x is the left child of p, make y as the left child of p.
5. Else allocate y as the right child of p.
6. Make y as the parent of x.
Right Rotate
In the right-rotation, the arrangement of the nodes on the left is changed into the arrangements on the right node.
- Let the underlying tree be:
2. On the off chance that x has a right subtree, assign y as the parent of the right subtree of x.
3. In the event that the parent of y is NULL, make x the root of the tree.
4. Else if y is the right child of its parent p, make x as the right child of p.
5. Else allocate x as the left child of p.
6. Make x as the parent of y.
Left-Right and Right-Left Rotate
In the left-right rotation, the arrangements are first moved to the left and afterward to the right.
- Do left rotation on x-y.
2. Do right rotation on y-z.
In the right-left rotation, the arrangements are first moved to the right and afterward to the left.
- Do right rotation on x-y.
2. Do left rotation on z-y.
Inserting an element into a Red-Black Tree
While inserting another node, the new hub is constantly inserted as a RED node. After insertion of another node, on the off chance that the tree is violating the properties of the red-black tree then, we do the accompanying activities.
- Recolor
2. Rotation
Algorithm to insert a node
Following steps are followed for inserting another element into a red-black tree:
- Let y b the leaf (ie. NIL) and x be the root of the tree.
2. Check if the tree is unfilled (ie. whether x is NIL). In the event that yes, insert newNode as a root node and color it black.
3. Else, repeat steps following steps until leaf (NIL) is reached.
a. Compare newKey and rootKey.
b. In the event that newKey is greater than rootKey, traverse through the right subtree.
c. Else traverse through the left subtree.
4. Allocate the parent of the leaf as a parent of newNode.
5. In the event that leafKey is greater than newKey, make newNode as rightChild.
6. Else, make newNode as leftChild.
7. Assign NULL to the left and rightChild of newNode.
8. Assign RED color to newNode.
9. Call InsertFix-algorithm to keep up the property of the red-black tree whenever violated.
Why newly inserted nodes are consistently red in a red-black tree?
This is on the grounds that inserting a red node doesn’t violate the depth property of a red-black tree.
In the event that you connect a red node to a red node, the standard is violated yet it is simpler to fix this issue than the issue presented by violating the depth property.
Algorithm to keep up the red-black property after insertion
This algorithm is used for keeping up the property of a red-black tree if the insertion of a newNode violates this property.
- Do the accompanying while the parent of newNode p is RED.
2. In the event that p is the left child of grandParent gP of z, do the accompanying.
Case-I:
a. On the off chance that the color of the right child of gP of z is RED, set the color of both the children of gP as BLACK and the color of gP as RED.
b. Assign gP to newNode.
Case-II:
c. Else in the event that newNode is the correct offspring of p, dole out p to newNode.
d. Left-Rotate newNode.
Case-III:
e. Set color of p as BLACK and color of gP as RED.
f. Right-Rotate gP.
3. Else, do the accompanying.
a. In the event that the color of the left child of gP of z is RED, set the color of both the children of gP as BLACK and the color of gP as RED.
b. Assign gP to newNode.
c. Else in the event that newNode is the left child of p, assign p to newNode and Right-Rotate newNode.
d. Set color of p as BLACK and color of gP as RED.
e. Left-Rotate gP.
4. Set the root of the tree as BLACK.
Deleting an element from a Red-Black Tree
This activity eliminates a node from the tree. Subsequent to erasing a node, the red-black property is looked after once more.
Algorithm to delete a node
- Save the color of nodeToBeDeleted in origrinalColor.
2. On the off chance that the left child of nodeToBeDeleted is NULL
a. Assign the right child of nodeToBeDeleted to x.
b.Transplant nodeToBeDeleted with x.
3. Else if the right child of nodeToBeDeleted is NULL
a. Assign the left child of nodeToBeDeleted into x.
b. Transplant nodeToBeDeleted with x.
4. Else
a. Assign the minimum of right subtree of noteToBeDeleted into y.
b. Save the color of y in originalColor.
c. Assign the rightChild of y into x.
d. On the off chance that y is a child of nodeToBeDeleted, set the parent of x as y.
e. Else, transplant y with rightChild of y.
f. Transplant nodeToBeDeleted with y.
g. Set the color of y with originalColor.
5. On the off chance that the originalColor is BLACK, call DeleteFix(x).
Algorithm to keep up Red-Black property after deletion
This algorithm is actualized when a black node is erased on the grounds that it violates the black depth property of the red-black tree.
This violation is corrected by assuming that node x (which is possessing y’s unique position) has an additional black. This makes node x neither red nor black. It is either doubly black or black-and-red. This violates the red-black properties.
Nonetheless, the color property of x isn’t changed rather the additional black is addressed in x’s highlighting the node.
The additional black can be taken out if
- It arrives at the root node.
2. In the event that x points to a red-black node. For this situation, x is colored black.
3. Appropriate rotations and recoloring are performed.
The accompanying algorithm holds the properties of a red-black tree.
- Do the following until the x is not the root of the tree and the color of x is BLACK
- If x is the left child of its parent then,
- Assign w to the sibling of x.
- If the right child of parent of x is RED,
Case-I:- Set the color of the right child of the parent of x as BLACK.
- Set the color of the parent of x as RED.
- Left-Rotate the parent of x.
- Assign the rightChild of the parent of x to w.
- If the color of both the right and the leftChild of w is BLACK,
Case-II:- Set the color of w as RED
- Assign the parent of x to x.
- Else if the color of the rightChild of w is BLACK
Case-III:- Set the color of the leftChild of w as BLACK
- Set the color of w as RED
- Right-Rotate w.
- Assign the rightChild of the parent of x to w.
- If any of the above cases do not occur, then do the following.
Case-IV:- Set the color of w as the color of the parent of x.
- Set the color of the parent of x as BLACK.
- Set the color of the right child of w as BLACK.
- Left-Rotate the parent of x.
- Set x as the root of the tree.
- Else the same as above with right changed to left and vice versa.
- Set the color of x as BLACK.
Python, Java and C/C++ Examples
Python
# Implementing Red-Black Tree in Python
import sys
# Node creation
class Node():
def __init__(self, item):
self.item = item
self.parent = None
self.left = None
self.right = None
self.color = 1
class RedBlackTree():
def __init__(self):
self.TNULL = Node(0)
self.TNULL.color = 0
self.TNULL.left = None
self.TNULL.right = None
self.root = self.TNULL
# Preorder
def pre_order_helper(self, node):
if node != TNULL:
sys.stdout.write(node.item + " ")
self.pre_order_helper(node.left)
self.pre_order_helper(node.right)
# Inorder
def in_order_helper(self, node):
if node != TNULL:
self.in_order_helper(node.left)
sys.stdout.write(node.item + " ")
self.in_order_helper(node.right)
# Postorder
def post_order_helper(self, node):
if node != TNULL:
self.post_order_helper(node.left)
self.post_order_helper(node.right)
sys.stdout.write(node.item + " ")
# Search the tree
def search_tree_helper(self, node, key):
if node == TNULL or key == node.item:
return node
if key < node.item:
return self.search_tree_helper(node.left, key)
return self.search_tree_helper(node.right, key)
# Balancing the tree after deletion
def delete_fix(self, x):
while x != self.root and x.color == 0:
if x == x.parent.left:
s = x.parent.right
if s.color == 1:
s.color = 0
x.parent.color = 1
self.left_rotate(x.parent)
s = x.parent.right
if s.left.color == 0 and s.right.color == 0:
s.color = 1
x = x.parent
else:
if s.right.color == 0:
s.left.color = 0
s.color = 1
self.right_rotate(s)
s = x.parent.right
s.color = x.parent.color
x.parent.color = 0
s.right.color = 0
self.left_rotate(x.parent)
x = self.root
else:
s = x.parent.left
if s.color == 1:
s.color = 0
x.parent.color = 1
self.right_rotate(x.parent)
s = x.parent.left
if s.right.color == 0 and s.right.color == 0:
s.color = 1
x = x.parent
else:
if s.left.color == 0:
s.right.color = 0
s.color = 1
self.left_rotate(s)
s = x.parent.left
s.color = x.parent.color
x.parent.color = 0
s.left.color = 0
self.right_rotate(x.parent)
x = self.root
x.color = 0
def __rb_transplant(self, u, v):
if u.parent == None:
self.root = v
elif u == u.parent.left:
u.parent.left = v
else:
u.parent.right = v
v.parent = u.parent
# Node deletion
def delete_node_helper(self, node, key):
z = self.TNULL
while node != self.TNULL:
if node.item == key:
z = node
if node.item <= key:
node = node.right
else:
node = node.left
if z == self.TNULL:
print("Cannot find key in the tree")
return
y = z
y_original_color = y.color
if z.left == self.TNULL:
x = z.right
self.__rb_transplant(z, z.right)
elif (z.right == self.TNULL):
x = z.left
self.__rb_transplant(z, z.left)
else:
y = self.minimum(z.right)
y_original_color = y.color
x = y.right
if y.parent == z:
x.parent = y
else:
self.__rb_transplant(y, y.right)
y.right = z.right
y.right.parent = y
self.__rb_transplant(z, y)
y.left = z.left
y.left.parent = y
y.color = z.color
if y_original_color == 0:
self.delete_fix(x)
# Balance the tree after insertion
def fix_insert(self, k):
while k.parent.color == 1:
if k.parent == k.parent.parent.right:
u = k.parent.parent.left
if u.color == 1:
u.color = 0
k.parent.color = 0
k.parent.parent.color = 1
k = k.parent.parent
else:
if k == k.parent.left:
k = k.parent
self.right_rotate(k)
k.parent.color = 0
k.parent.parent.color = 1
self.left_rotate(k.parent.parent)
else:
u = k.parent.parent.right
if u.color == 1:
u.color = 0
k.parent.color = 0
k.parent.parent.color = 1
k = k.parent.parent
else:
if k == k.parent.right:
k = k.parent
self.left_rotate(k)
k.parent.color = 0
k.parent.parent.color = 1
self.right_rotate(k.parent.parent)
if k == self.root:
break
self.root.color = 0
# Printing the tree
def __print_helper(self, node, indent, last):
if node != self.TNULL:
sys.stdout.write(indent)
if last:
sys.stdout.write("R----")
indent += " "
else:
sys.stdout.write("L----")
indent += "| "
s_color = "RED" if node.color == 1 else "BLACK"
print(str(node.item) + "(" + s_color + ")")
self.__print_helper(node.left, indent, False)
self.__print_helper(node.right, indent, True)
def preorder(self):
self.pre_order_helper(self.root)
def inorder(self):
self.in_order_helper(self.root)
def postorder(self):
self.post_order_helper(self.root)
def searchTree(self, k):
return self.search_tree_helper(self.root, k)
def minimum(self, node):
while node.left != self.TNULL:
node = node.left
return node
def maximum(self, node):
while node.right != self.TNULL:
node = node.right
return node
def successor(self, x):
if x.right != self.TNULL:
return self.minimum(x.right)
y = x.parent
while y != self.TNULL and x == y.right:
x = y
y = y.parent
return y
def predecessor(self, x):
if (x.left != self.TNULL):
return self.maximum(x.left)
y = x.parent
while y != self.TNULL and x == y.left:
x = y
y = y.parent
return y
def left_rotate(self, x):
y = x.right
x.right = y.left
if y.left != self.TNULL:
y.left.parent = x
y.parent = x.parent
if x.parent == None:
self.root = y
elif x == x.parent.left:
x.parent.left = y
else:
x.parent.right = y
y.left = x
x.parent = y
def right_rotate(self, x):
y = x.left
x.left = y.right
if y.right != self.TNULL:
y.right.parent = x
y.parent = x.parent
if x.parent == None:
self.root = y
elif x == x.parent.right:
x.parent.right = y
else:
x.parent.left = y
y.right = x
x.parent = y
def insert(self, key):
node = Node(key)
node.parent = None
node.item = key
node.left = self.TNULL
node.right = self.TNULL
node.color = 1
y = None
x = self.root
while x != self.TNULL:
y = x
if node.item < x.item:
x = x.left
else:
x = x.right
node.parent = y
if y == None:
self.root = node
elif node.item < y.item:
y.left = node
else:
y.right = node
if node.parent == None:
node.color = 0
return
if node.parent.parent == None:
return
self.fix_insert(node)
def get_root(self):
return self.root
def delete_node(self, item):
self.delete_node_helper(self.root, item)
def print_tree(self):
self.__print_helper(self.root, "", True)
if __name__ == "__main__":
bst = RedBlackTree()
bst.insert(55)
bst.insert(40)
bst.insert(65)
bst.insert(60)
bst.insert(75)
bst.insert(57)
bst.print_tree()
print("\nAfter deleting an element")
bst.delete_node(40)
bst.print_tree()
Java
// Implementing Red-Black Tree in Java
class Node {
int data;
Node parent;
Node left;
Node right;
int color;
}
public class RedBlackTree {
private Node root;
private Node TNULL;
// Preorder
private void preOrderHelper(Node node) {
if (node != TNULL) {
System.out.print(node.data + " ");
preOrderHelper(node.left);
preOrderHelper(node.right);
}
}
// Inorder
private void inOrderHelper(Node node) {
if (node != TNULL) {
inOrderHelper(node.left);
System.out.print(node.data + " ");
inOrderHelper(node.right);
}
}
// Post order
private void postOrderHelper(Node node) {
if (node != TNULL) {
postOrderHelper(node.left);
postOrderHelper(node.right);
System.out.print(node.data + " ");
}
}
// Search the tree
private Node searchTreeHelper(Node node, int key) {
if (node == TNULL || key == node.data) {
return node;
}
if (key < node.data) {
return searchTreeHelper(node.left, key);
}
return searchTreeHelper(node.right, key);
}
// Balance the tree after deletion of a node
private void fixDelete(Node x) {
Node s;
while (x != root && x.color == 0) {
if (x == x.parent.left) {
s = x.parent.right;
if (s.color == 1) {
s.color = 0;
x.parent.color = 1;
leftRotate(x.parent);
s = x.parent.right;
}
if (s.left.color == 0 && s.right.color == 0) {
s.color = 1;
x = x.parent;
} else {
if (s.right.color == 0) {
s.left.color = 0;
s.color = 1;
rightRotate(s);
s = x.parent.right;
}
s.color = x.parent.color;
x.parent.color = 0;
s.right.color = 0;
leftRotate(x.parent);
x = root;
}
} else {
s = x.parent.left;
if (s.color == 1) {
s.color = 0;
x.parent.color = 1;
rightRotate(x.parent);
s = x.parent.left;
}
if (s.right.color == 0 && s.right.color == 0) {
s.color = 1;
x = x.parent;
} else {
if (s.left.color == 0) {
s.right.color = 0;
s.color = 1;
leftRotate(s);
s = x.parent.left;
}
s.color = x.parent.color;
x.parent.color = 0;
s.left.color = 0;
rightRotate(x.parent);
x = root;
}
}
}
x.color = 0;
}
private void rbTransplant(Node u, Node v) {
if (u.parent == null) {
root = v;
} else if (u == u.parent.left) {
u.parent.left = v;
} else {
u.parent.right = v;
}
v.parent = u.parent;
}
private void deleteNodeHelper(Node node, int key) {
Node z = TNULL;
Node x, y;
while (node != TNULL) {
if (node.data == key) {
z = node;
}
if (node.data <= key) {
node = node.right;
} else {
node = node.left;
}
}
if (z == TNULL) {
System.out.println("Couldn't find key in the tree");
return;
}
y = z;
int yOriginalColor = y.color;
if (z.left == TNULL) {
x = z.right;
rbTransplant(z, z.right);
} else if (z.right == TNULL) {
x = z.left;
rbTransplant(z, z.left);
} else {
y = minimum(z.right);
yOriginalColor = y.color;
x = y.right;
if (y.parent == z) {
x.parent = y;
} else {
rbTransplant(y, y.right);
y.right = z.right;
y.right.parent = y;
}
rbTransplant(z, y);
y.left = z.left;
y.left.parent = y;
y.color = z.color;
}
if (yOriginalColor == 0) {
fixDelete(x);
}
}
// Balance the node after insertion
private void fixInsert(Node k) {
Node u;
while (k.parent.color == 1) {
if (k.parent == k.parent.parent.right) {
u = k.parent.parent.left;
if (u.color == 1) {
u.color = 0;
k.parent.color = 0;
k.parent.parent.color = 1;
k = k.parent.parent;
} else {
if (k == k.parent.left) {
k = k.parent;
rightRotate(k);
}
k.parent.color = 0;
k.parent.parent.color = 1;
leftRotate(k.parent.parent);
}
} else {
u = k.parent.parent.right;
if (u.color == 1) {
u.color = 0;
k.parent.color = 0;
k.parent.parent.color = 1;
k = k.parent.parent;
} else {
if (k == k.parent.right) {
k = k.parent;
leftRotate(k);
}
k.parent.color = 0;
k.parent.parent.color = 1;
rightRotate(k.parent.parent);
}
}
if (k == root) {
break;
}
}
root.color = 0;
}
private void printHelper(Node root, String indent, boolean last) {
if (root != TNULL) {
System.out.print(indent);
if (last) {
System.out.print("R----");
indent += " ";
} else {
System.out.print("L----");
indent += "| ";
}
String sColor = root.color == 1 ? "RED" : "BLACK";
System.out.println(root.data + "(" + sColor + ")");
printHelper(root.left, indent, false);
printHelper(root.right, indent, true);
}
}
public RedBlackTree() {
TNULL = new Node();
TNULL.color = 0;
TNULL.left = null;
TNULL.right = null;
root = TNULL;
}
public void preorder() {
preOrderHelper(this.root);
}
public void inorder() {
inOrderHelper(this.root);
}
public void postorder() {
postOrderHelper(this.root);
}
public Node searchTree(int k) {
return searchTreeHelper(this.root, k);
}
public Node minimum(Node node) {
while (node.left != TNULL) {
node = node.left;
}
return node;
}
public Node maximum(Node node) {
while (node.right != TNULL) {
node = node.right;
}
return node;
}
public Node successor(Node x) {
if (x.right != TNULL) {
return minimum(x.right);
}
Node y = x.parent;
while (y != TNULL && x == y.right) {
x = y;
y = y.parent;
}
return y;
}
public Node predecessor(Node x) {
if (x.left != TNULL) {
return maximum(x.left);
}
Node y = x.parent;
while (y != TNULL && x == y.left) {
x = y;
y = y.parent;
}
return y;
}
public void leftRotate(Node x) {
Node y = x.right;
x.right = y.left;
if (y.left != TNULL) {
y.left.parent = x;
}
y.parent = x.parent;
if (x.parent == null) {
this.root = y;
} else if (x == x.parent.left) {
x.parent.left = y;
} else {
x.parent.right = y;
}
y.left = x;
x.parent = y;
}
public void rightRotate(Node x) {
Node y = x.left;
x.left = y.right;
if (y.right != TNULL) {
y.right.parent = x;
}
y.parent = x.parent;
if (x.parent == null) {
this.root = y;
} else if (x == x.parent.right) {
x.parent.right = y;
} else {
x.parent.left = y;
}
y.right = x;
x.parent = y;
}
public void insert(int key) {
Node node = new Node();
node.parent = null;
node.data = key;
node.left = TNULL;
node.right = TNULL;
node.color = 1;
Node y = null;
Node x = this.root;
while (x != TNULL) {
y = x;
if (node.data < x.data) {
x = x.left;
} else {
x = x.right;
}
}
node.parent = y;
if (y == null) {
root = node;
} else if (node.data < y.data) {
y.left = node;
} else {
y.right = node;
}
if (node.parent == null) {
node.color = 0;
return;
}
if (node.parent.parent == null) {
return;
}
fixInsert(node);
}
public Node getRoot() {
return this.root;
}
public void deleteNode(int data) {
deleteNodeHelper(this.root, data);
}
public void printTree() {
printHelper(this.root, "", true);
}
public static void main(String[] args) {
RedBlackTree bst = new RedBlackTree();
bst.insert(55);
bst.insert(40);
bst.insert(65);
bst.insert(60);
bst.insert(75);
bst.insert(57);
bst.printTree();
System.out.println("\nAfter deleting:");
bst.deleteNode(40);
bst.printTree();
}
}
C
// Implementing Red-Black Tree in C
#include <stdio.h>
#include <stdlib.h>
enum nodeColor {
RED,
BLACK
};
struct rbNode {
int data, color;
struct rbNode *link[2];
};
struct rbNode *root = NULL;
// Create a red-black tree
struct rbNode *createNode(int data) {
struct rbNode *newnode;
newnode = (struct rbNode *)malloc(sizeof(struct rbNode));
newnode->data = data;
newnode->color = RED;
newnode->link[0] = newnode->link[1] = NULL;
return newnode;
}
// Insert an node
void insertion(int data) {
struct rbNode *stack[98], *ptr, *newnode, *xPtr, *yPtr;
int dir[98], ht = 0, index;
ptr = root;
if (!root) {
root = createNode(data);
return;
}
stack[ht] = root;
dir[ht++] = 0;
while (ptr != NULL) {
if (ptr->data == data) {
printf("Duplicates Not Allowed!!\n");
return;
}
index = (data - ptr->data) > 0 ? 1 : 0;
stack[ht] = ptr;
ptr = ptr->link[index];
dir[ht++] = index;
}
stack[ht - 1]->link[index] = newnode = createNode(data);
while ((ht >= 3) && (stack[ht - 1]->color == RED)) {
if (dir[ht - 2] == 0) {
yPtr = stack[ht - 2]->link[1];
if (yPtr != NULL && yPtr->color == RED) {
stack[ht - 2]->color = RED;
stack[ht - 1]->color = yPtr->color = BLACK;
ht = ht - 2;
} else {
if (dir[ht - 1] == 0) {
yPtr = stack[ht - 1];
} else {
xPtr = stack[ht - 1];
yPtr = xPtr->link[1];
xPtr->link[1] = yPtr->link[0];
yPtr->link[0] = xPtr;
stack[ht - 2]->link[0] = yPtr;
}
xPtr = stack[ht - 2];
xPtr->color = RED;
yPtr->color = BLACK;
xPtr->link[0] = yPtr->link[1];
yPtr->link[1] = xPtr;
if (xPtr == root) {
root = yPtr;
} else {
stack[ht - 3]->link[dir[ht - 3]] = yPtr;
}
break;
}
} else {
yPtr = stack[ht - 2]->link[0];
if ((yPtr != NULL) && (yPtr->color == RED)) {
stack[ht - 2]->color = RED;
stack[ht - 1]->color = yPtr->color = BLACK;
ht = ht - 2;
} else {
if (dir[ht - 1] == 1) {
yPtr = stack[ht - 1];
} else {
xPtr = stack[ht - 1];
yPtr = xPtr->link[0];
xPtr->link[0] = yPtr->link[1];
yPtr->link[1] = xPtr;
stack[ht - 2]->link[1] = yPtr;
}
xPtr = stack[ht - 2];
yPtr->color = BLACK;
xPtr->color = RED;
xPtr->link[1] = yPtr->link[0];
yPtr->link[0] = xPtr;
if (xPtr == root) {
root = yPtr;
} else {
stack[ht - 3]->link[dir[ht - 3]] = yPtr;
}
break;
}
}
}
root->color = BLACK;
}
// Delete a node
void deletion(int data) {
struct rbNode *stack[98], *ptr, *xPtr, *yPtr;
struct rbNode *pPtr, *qPtr, *rPtr;
int dir[98], ht = 0, diff, i;
enum nodeColor color;
if (!root) {
printf("Tree not available\n");
return;
}
ptr = root;
while (ptr != NULL) {
if ((data - ptr->data) == 0)
break;
diff = (data - ptr->data) > 0 ? 1 : 0;
stack[ht] = ptr;
dir[ht++] = diff;
ptr = ptr->link[diff];
}
if (ptr->link[1] == NULL) {
if ((ptr == root) && (ptr->link[0] == NULL)) {
free(ptr);
root = NULL;
} else if (ptr == root) {
root = ptr->link[0];
free(ptr);
} else {
stack[ht - 1]->link[dir[ht - 1]] = ptr->link[0];
}
} else {
xPtr = ptr->link[1];
if (xPtr->link[0] == NULL) {
xPtr->link[0] = ptr->link[0];
color = xPtr->color;
xPtr->color = ptr->color;
ptr->color = color;
if (ptr == root) {
root = xPtr;
} else {
stack[ht - 1]->link[dir[ht - 1]] = xPtr;
}
dir[ht] = 1;
stack[ht++] = xPtr;
} else {
i = ht++;
while (1) {
dir[ht] = 0;
stack[ht++] = xPtr;
yPtr = xPtr->link[0];
if (!yPtr->link[0])
break;
xPtr = yPtr;
}
dir[i] = 1;
stack[i] = yPtr;
if (i > 0)
stack[i - 1]->link[dir[i - 1]] = yPtr;
yPtr->link[0] = ptr->link[0];
xPtr->link[0] = yPtr->link[1];
yPtr->link[1] = ptr->link[1];
if (ptr == root) {
root = yPtr;
}
color = yPtr->color;
yPtr->color = ptr->color;
ptr->color = color;
}
}
if (ht < 1)
return;
if (ptr->color == BLACK) {
while (1) {
pPtr = stack[ht - 1]->link[dir[ht - 1]];
if (pPtr && pPtr->color == RED) {
pPtr->color = BLACK;
break;
}
if (ht < 2)
break;
if (dir[ht - 2] == 0) {
rPtr = stack[ht - 1]->link[1];
if (!rPtr)
break;
if (rPtr->color == RED) {
stack[ht - 1]->color = RED;
rPtr->color = BLACK;
stack[ht - 1]->link[1] = rPtr->link[0];
rPtr->link[0] = stack[ht - 1];
if (stack[ht - 1] == root) {
root = rPtr;
} else {
stack[ht - 2]->link[dir[ht - 2]] = rPtr;
}
dir[ht] = 0;
stack[ht] = stack[ht - 1];
stack[ht - 1] = rPtr;
ht++;
rPtr = stack[ht - 1]->link[1];
}
if ((!rPtr->link[0] || rPtr->link[0]->color == BLACK) &&
(!rPtr->link[1] || rPtr->link[1]->color == BLACK)) {
rPtr->color = RED;
} else {
if (!rPtr->link[1] || rPtr->link[1]->color == BLACK) {
qPtr = rPtr->link[0];
rPtr->color = RED;
qPtr->color = BLACK;
rPtr->link[0] = qPtr->link[1];
qPtr->link[1] = rPtr;
rPtr = stack[ht - 1]->link[1] = qPtr;
}
rPtr->color = stack[ht - 1]->color;
stack[ht - 1]->color = BLACK;
rPtr->link[1]->color = BLACK;
stack[ht - 1]->link[1] = rPtr->link[0];
rPtr->link[0] = stack[ht - 1];
if (stack[ht - 1] == root) {
root = rPtr;
} else {
stack[ht - 2]->link[dir[ht - 2]] = rPtr;
}
break;
}
} else {
rPtr = stack[ht - 1]->link[0];
if (!rPtr)
break;
if (rPtr->color == RED) {
stack[ht - 1]->color = RED;
rPtr->color = BLACK;
stack[ht - 1]->link[0] = rPtr->link[1];
rPtr->link[1] = stack[ht - 1];
if (stack[ht - 1] == root) {
root = rPtr;
} else {
stack[ht - 2]->link[dir[ht - 2]] = rPtr;
}
dir[ht] = 1;
stack[ht] = stack[ht - 1];
stack[ht - 1] = rPtr;
ht++;
rPtr = stack[ht - 1]->link[0];
}
if ((!rPtr->link[0] || rPtr->link[0]->color == BLACK) &&
(!rPtr->link[1] || rPtr->link[1]->color == BLACK)) {
rPtr->color = RED;
} else {
if (!rPtr->link[0] || rPtr->link[0]->color == BLACK) {
qPtr = rPtr->link[1];
rPtr->color = RED;
qPtr->color = BLACK;
rPtr->link[1] = qPtr->link[0];
qPtr->link[0] = rPtr;
rPtr = stack[ht - 1]->link[0] = qPtr;
}
rPtr->color = stack[ht - 1]->color;
stack[ht - 1]->color = BLACK;
rPtr->link[0]->color = BLACK;
stack[ht - 1]->link[0] = rPtr->link[1];
rPtr->link[1] = stack[ht - 1];
if (stack[ht - 1] == root) {
root = rPtr;
} else {
stack[ht - 2]->link[dir[ht - 2]] = rPtr;
}
break;
}
}
ht--;
}
}
}
// Print the inorder traversal of the tree
void inorderTraversal(struct rbNode *node) {
if (node) {
inorderTraversal(node->link[0]);
printf("%d ", node->data);
inorderTraversal(node->link[1]);
}
return;
}
// Driver code
int main() {
int ch, data;
while (1) {
printf("1. Insertion\t2. Deletion\n");
printf("3. Traverse\t4. Exit");
printf("\nEnter your choice:");
scanf("%d", &ch);
switch (ch) {
case 1:
printf("Enter the element to insert:");
scanf("%d", &data);
insertion(data);
break;
case 2:
printf("Enter the element to delete:");
scanf("%d", &data);
deletion(data);
break;
case 3:
inorderTraversal(root);
printf("\n");
break;
case 4:
exit(0);
default:
printf("Not available\n");
break;
}
printf("\n");
}
return 0;
}
C++
// Implementing Red-Black Tree in C++
#include <iostream>
using namespace std;
struct Node {
int data;
Node *parent;
Node *left;
Node *right;
int color;
};
typedef Node *NodePtr;
class RedBlackTree {
private:
NodePtr root;
NodePtr TNULL;
void initializeNULLNode(NodePtr node, NodePtr parent) {
node->data = 0;
node->parent = parent;
node->left = nullptr;
node->right = nullptr;
node->color = 0;
}
// Preorder
void preOrderHelper(NodePtr node) {
if (node != TNULL) {
cout << node->data << " ";
preOrderHelper(node->left);
preOrderHelper(node->right);
}
}
// Inorder
void inOrderHelper(NodePtr node) {
if (node != TNULL) {
inOrderHelper(node->left);
cout << node->data << " ";
inOrderHelper(node->right);
}
}
// Post order
void postOrderHelper(NodePtr node) {
if (node != TNULL) {
postOrderHelper(node->left);
postOrderHelper(node->right);
cout << node->data << " ";
}
}
NodePtr searchTreeHelper(NodePtr node, int key) {
if (node == TNULL || key == node->data) {
return node;
}
if (key < node->data) {
return searchTreeHelper(node->left, key);
}
return searchTreeHelper(node->right, key);
}
// For balancing the tree after deletion
void deleteFix(NodePtr x) {
NodePtr s;
while (x != root && x->color == 0) {
if (x == x->parent->left) {
s = x->parent->right;
if (s->color == 1) {
s->color = 0;
x->parent->color = 1;
leftRotate(x->parent);
s = x->parent->right;
}
if (s->left->color == 0 && s->right->color == 0) {
s->color = 1;
x = x->parent;
} else {
if (s->right->color == 0) {
s->left->color = 0;
s->color = 1;
rightRotate(s);
s = x->parent->right;
}
s->color = x->parent->color;
x->parent->color = 0;
s->right->color = 0;
leftRotate(x->parent);
x = root;
}
} else {
s = x->parent->left;
if (s->color == 1) {
s->color = 0;
x->parent->color = 1;
rightRotate(x->parent);
s = x->parent->left;
}
if (s->right->color == 0 && s->right->color == 0) {
s->color = 1;
x = x->parent;
} else {
if (s->left->color == 0) {
s->right->color = 0;
s->color = 1;
leftRotate(s);
s = x->parent->left;
}
s->color = x->parent->color;
x->parent->color = 0;
s->left->color = 0;
rightRotate(x->parent);
x = root;
}
}
}
x->color = 0;
}
void rbTransplant(NodePtr u, NodePtr v) {
if (u->parent == nullptr) {
root = v;
} else if (u == u->parent->left) {
u->parent->left = v;
} else {
u->parent->right = v;
}
v->parent = u->parent;
}
void deleteNodeHelper(NodePtr node, int key) {
NodePtr z = TNULL;
NodePtr x, y;
while (node != TNULL) {
if (node->data == key) {
z = node;
}
if (node->data <= key) {
node = node->right;
} else {
node = node->left;
}
}
if (z == TNULL) {
cout << "Key not found in the tree" << endl;
return;
}
y = z;
int y_original_color = y->color;
if (z->left == TNULL) {
x = z->right;
rbTransplant(z, z->right);
} else if (z->right == TNULL) {
x = z->left;
rbTransplant(z, z->left);
} else {
y = minimum(z->right);
y_original_color = y->color;
x = y->right;
if (y->parent == z) {
x->parent = y;
} else {
rbTransplant(y, y->right);
y->right = z->right;
y->right->parent = y;
}
rbTransplant(z, y);
y->left = z->left;
y->left->parent = y;
y->color = z->color;
}
delete z;
if (y_original_color == 0) {
deleteFix(x);
}
}
// For balancing the tree after insertion
void insertFix(NodePtr k) {
NodePtr u;
while (k->parent->color == 1) {
if (k->parent == k->parent->parent->right) {
u = k->parent->parent->left;
if (u->color == 1) {
u->color = 0;
k->parent->color = 0;
k->parent->parent->color = 1;
k = k->parent->parent;
} else {
if (k == k->parent->left) {
k = k->parent;
rightRotate(k);
}
k->parent->color = 0;
k->parent->parent->color = 1;
leftRotate(k->parent->parent);
}
} else {
u = k->parent->parent->right;
if (u->color == 1) {
u->color = 0;
k->parent->color = 0;
k->parent->parent->color = 1;
k = k->parent->parent;
} else {
if (k == k->parent->right) {
k = k->parent;
leftRotate(k);
}
k->parent->color = 0;
k->parent->parent->color = 1;
rightRotate(k->parent->parent);
}
}
if (k == root) {
break;
}
}
root->color = 0;
}
void printHelper(NodePtr root, string indent, bool last) {
if (root != TNULL) {
cout << indent;
if (last) {
cout << "R----";
indent += " ";
} else {
cout << "L----";
indent += "| ";
}
string sColor = root->color ? "RED" : "BLACK";
cout << root->data << "(" << sColor << ")" << endl;
printHelper(root->left, indent, false);
printHelper(root->right, indent, true);
}
}
public:
RedBlackTree() {
TNULL = new Node;
TNULL->color = 0;
TNULL->left = nullptr;
TNULL->right = nullptr;
root = TNULL;
}
void preorder() {
preOrderHelper(this->root);
}
void inorder() {
inOrderHelper(this->root);
}
void postorder() {
postOrderHelper(this->root);
}
NodePtr searchTree(int k) {
return searchTreeHelper(this->root, k);
}
NodePtr minimum(NodePtr node) {
while (node->left != TNULL) {
node = node->left;
}
return node;
}
NodePtr maximum(NodePtr node) {
while (node->right != TNULL) {
node = node->right;
}
return node;
}
NodePtr successor(NodePtr x) {
if (x->right != TNULL) {
return minimum(x->right);
}
NodePtr y = x->parent;
while (y != TNULL && x == y->right) {
x = y;
y = y->parent;
}
return y;
}
NodePtr predecessor(NodePtr x) {
if (x->left != TNULL) {
return maximum(x->left);
}
NodePtr y = x->parent;
while (y != TNULL && x == y->left) {
x = y;
y = y->parent;
}
return y;
}
void leftRotate(NodePtr x) {
NodePtr y = x->right;
x->right = y->left;
if (y->left != TNULL) {
y->left->parent = x;
}
y->parent = x->parent;
if (x->parent == nullptr) {
this->root = y;
} else if (x == x->parent->left) {
x->parent->left = y;
} else {
x->parent->right = y;
}
y->left = x;
x->parent = y;
}
void rightRotate(NodePtr x) {
NodePtr y = x->left;
x->left = y->right;
if (y->right != TNULL) {
y->right->parent = x;
}
y->parent = x->parent;
if (x->parent == nullptr) {
this->root = y;
} else if (x == x->parent->right) {
x->parent->right = y;
} else {
x->parent->left = y;
}
y->right = x;
x->parent = y;
}
// Inserting a node
void insert(int key) {
NodePtr node = new Node;
node->parent = nullptr;
node->data = key;
node->left = TNULL;
node->right = TNULL;
node->color = 1;
NodePtr y = nullptr;
NodePtr x = this->root;
while (x != TNULL) {
y = x;
if (node->data < x->data) {
x = x->left;
} else {
x = x->right;
}
}
node->parent = y;
if (y == nullptr) {
root = node;
} else if (node->data < y->data) {
y->left = node;
} else {
y->right = node;
}
if (node->parent == nullptr) {
node->color = 0;
return;
}
if (node->parent->parent == nullptr) {
return;
}
insertFix(node);
}
NodePtr getRoot() {
return this->root;
}
void deleteNode(int data) {
deleteNodeHelper(this->root, data);
}
void printTree() {
if (root) {
printHelper(this->root, "", true);
}
}
};
int main() {
RedBlackTree bst;
bst.insert(55);
bst.insert(40);
bst.insert(65);
bst.insert(60);
bst.insert(75);
bst.insert(57);
bst.printTree();
cout << endl
<< "After deleting" << endl;
bst.deleteNode(40);
bst.printTree();
}
Red-Black Tree Applications
- To actualize finite maps
- To execute Java package: java.util.TreeMap and java.util.TreeSet
- To actualize Standard Template Libraries (STL) in C++: multiset, map, multimap
- In Linux Kernel
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