https://leetcode.com/problems/delete-node-in-a-bst/

1. Use recursion:

  1. //36 ms    15.5 MB
  3. /**
  4.  * Definition for a binary tree node.
  5.  * struct TreeNode {
  6.  *     int val;
  7.  *     TreeNode *left;
  8.  *     TreeNode *right;
  9.  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
  10.  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
  11.  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
  12.  * };
  13.  */
  14. class Solution {
  15. public:
  16.     TreeNode* deleteNode(TreeNode* root, int key) {
  17.         if (!root) return root;
  19.         if (key > root->val) {
  20.             root->right = deleteNode(root->right, key);
  21.         } else if (key < root->val) {
  22.             root->left = deleteNode(root->left, key);
  23.         } else {
  24.             if (root->left && root->right) {
  25.                 TreeNode* min = root->right;
  26.                 while (min->left) 
  27.                     min = min->left;
  29.                 root->val = min->val;
  30.                 root->right = deleteNode(root->right, min->val);
  31.             } else {
  32.                 TreeNode* new_root;
  33.                 if(root->left == NULL){
  34.                     new_root = root->right;
  35.                 } else {
  36.                     new_root = root->left;
  37.                 }
  38.                 root->left = NULL;
  39.                 root->right = NULL;
  41.                 delete root;
  42.                 return new_root;
  43.             }
  44.         }    
  46.         return root;
  47.     }
  48. };