450. Delete Node in a BST（在二叉树搜索树中删除节点）

题目描述

方法思路

class Solution {
    //Runtime: 3 ms, faster than 98.89%
    //Memory Usage: 41.4 MB, less than 35.22%
    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 if(root.left != null && root.right != null){
            //这里也可以找左子树的最大值来解决双子树的问题
            root.val = findMin(root.right).val;
            root.right = deleteNode(root.right, root.val);
        }else
            //此时目标节点只有一个子树或者没有子树，问题变得简单起来
            root = (root.left != null) ? root.left : root.right;
        
        return root;
    }
    
    public TreeNode findMin(TreeNode root){
        if(root == null) return root;
        TreeNode cur = root;
        while(cur.left != null)
            cur = cur.left;
        return cur;
    }
}