Delete a node from BST

Problem Statement - link #

Given a Binary Search Tree and a node value X. Delete the node with the given value X from the BST. If no node with value x exists, then do not make any change.

Your Task: You don’t need to read input or print anything. Your task is to complete the function deleteNode() which takes two arguments. The first being the root of the tree, and an integer ‘X’ denoting the node value to be deleted from the BST. Return the root of the BST after deleting the node with value X. Do not make any update if there’s no node with value X present in the BST.

Note: The generated output will be the inorder traversal of the modified tree.

Expected Time Complexity: O(h)
Expected Auxiliary Space: O(h)

Examples #

Example 1:

Input:
            1
             \
              2
                \
                 8 
               /    \
              5      11
            /  \    /  \
           4    7  9   12
X = 9
Output: 1 2 4 5 7 8 11 12
Explanation: In the given input tree after
deleting 9 will be
             1
              \
               2
                 \
                  8
                 /   \
                5     11
               /  \     \
              4    7     12

Example 2:

Input:
      2
    /   \
   1     3
X = 12
Output: 1 2 3
Explanation: In the given input there
is no node with value 12 , so the tree
will remain same.

Constraints #

• 1 <= Number of nodes <= 10^5

Solutions #

// Function to delete a node from BST.
Node *deleteNode(Node *root, int X) {
    // your code goes here
    if(!root) return NULL;
    if(root->data > X) root->left = deleteNode(root->left,X);
    else if(root->data < X) root->right = deleteNode(root->right,X);
    else{
        if(!root->left&&!root->right) { delete root ; return NULL;}
        if(!root->left) {
            Node* temp = root->right;
            delete root; return temp;
        }
        if(!root->right) {
            Node* temp = root->left;
            delete root; return temp;
        }
        Node* temp = root->right;
        while(temp->left) temp=temp->left;
        root->data = temp->data;
        root->right = deleteNode(root->right, temp->data);

    } 
    return root;
}