450. Delete Node in a BST

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:

1. Search for a node to remove.
2. 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   7Given 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       7Another valid answer is [5,2,6,null,4,null,7].    5   / \  2   6   \   \    4   7

思路：记得是在去面试WAP的高铁上补得LC的题

package l450;/* * 有返回值一样可以递归 */class Solution {    public TreeNode deleteNode(TreeNode root, int key) {        if(root == null)return null;            if(root.val < key)root.right = deleteNode(root.right, key);    else if(root.val > key)root.left =  deleteNode(root.left, key);    else {    TreeNode rightSmallest = root.right;            if(rightSmallest == null)return root.left;    while(rightSmallest.left != null)    rightSmallest = rightSmallest.left;        rightSmallest.left = root.left;    return root.right;    }        return root;    }}