# LeetCode - 0450. Delete Node in a BST
### 題目網址：https://leetcode.com/problems/delete-node-in-a-bst/
###### tags: `LeetCode` `Medium` `圖論`

/*
    -LeetCode format-
    Problem: 450. Delete Node in a BST
    Difficulty: Medium
    
    by Inversionpeter
*/



/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    TreeNode* deleteNode(TreeNode* root, int key) {
        if (!root)
            return nullptr;
        if (root->val == key) {
            if (!root->left && !root->right)
                return nullptr;
            if (!root->right)
                return root->left;
            if (!root->left)
                return root->right;
            TreeNode *nowAt = root->left, *parent = root;
            while (nowAt->right) {
                parent = nowAt;
                nowAt = nowAt->right;
            }
            root->val = nowAt->val;
            if (parent->left == nowAt)
                parent->left = nowAt->left;
            else
                parent->right = nowAt->left;
        }
        else if (root->val > key)
            root->left = deleteNode(root->left, key);
        else 
            root->right = deleteNode(root->right, key);
        return root;
    }
};