#450 - Delete Node in a BST

Medium • View on LeetCode • View on GitHub

Problem Description

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.

Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} key
 * @return {TreeNode}
 */
var deleteNode = function(root, key) {
  if (!root) return root;
  if (root.val < key) {
    root.right = deleteNode(root.right, key);
  } else if (root.val > key) {
    root.left = deleteNode(root.left, key);
  } else {
    if (root.left === null) {
      return root.right;
    } else if (root.right === null) {
      return root.left;
    } else {
      let node = root.right;
      while (node.left) {
        node = node.left;
      }
      node.left = root.left;
      return root.right;
    }
  }
  return root;
};