450. Delete Node in a BST

Question

Given a root node reference of a BST and a key, delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST.

Basically, the deletion can be divided into two stages:

Search for a node to remove. If the node is found, delete the node. Note: Time complexity should be O(height of tree).

Example:

root = [5,3,6,2,4,null,7]
key = 3

    5
   / \
  3   6
 / \   \
2   4   7

Given key to delete is 3. So we find the node with value 3 and delete it.

One valid answer is [5,4,6,2,null,null,7], shown in the following BST.

    5
   / \
  4   6
 /     \
2       7

Another valid answer is [5,2,6,null,4,null,7].

    5
   / \
  2   6
   \   \
    4   7

Solution

  • Method 1: recursion Imgur ```Java /**
    • Definition for a binary tree node.
    • public class TreeNode {
    • int val;
    • TreeNode left;
    • TreeNode right;
    • TreeNode(int x) { val = x; }
    • } */ class Solution { public TreeNode deleteNode(TreeNode root, int key) { if(root == null) return root; if(key < root.val) root.left = deleteNode(root.left, key); else if(key > root.val) root.right = deleteNode(root.right, key); else{ TreeNode res = null; if(root.left == null) res = root.right; else if(root.right == null) res = root.left; else{ // both left and right are not null. TreeNode parent = root; res = root.right; while(res.left != null){ parent = res; res = res.left; } if(parent != root){ parent.left = res.right; res.right = root.right; } res.left = root.left; } return res; } return root; } } ```

Reference

  1. 花花酱 LeetCode 450. Delete Node in a BST