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:

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

一刷
题解：
这题用recursive做最适合。因为如果要删除的点同时拥有左子树和右子树，然而又要删去right子树中的leftmost

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode deleteNode(TreeNode root, int key) {
       if(root == null) return null;
        if(key<root.val) root.left = deleteNode(root.left, key);
        else if(key > root.val) root.right = deleteNode(root.right, key);
        else{
            if(root.left == null) return root.right;
            else if(root.right == null) return root.left;
            TreeNode minNode = findMin(root.right);
            root.val = minNode.val;
            root.right = deleteNode(root.right, root.val);
        }
        return root;
    }
    
    
    private TreeNode findMin(TreeNode root){
        while(root.left!=null) root = root.left;
        return root;
    }
        
}