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

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    TreeNode* deleteNode(TreeNode* root, int key) {        if (root == NULL) {            return NULL;        }        TreeNode* cur = root;        TreeNode* last = NULL;        while (cur != NULL && cur->val != key) {            if (cur->val > key) {                last = cur;                cur = cur->left;            }            else {                last = cur;                cur = cur->right;            }        }        if (cur == NULL) {            return root;        }        TreeNode* tlast = cur;        TreeNode* tcur;        if (cur->left != NULL) {            tcur = cur->left;            while (tcur->right != NULL) {                tlast = tcur;                tcur = tcur->right;            }            if (tcur == tlast->left) {                tlast->left = tcur->left;            }            else {                tlast->right = tcur->left;            }            cur->val = tcur->val;        }        else if (cur->right != NULL) {            tcur = cur->right;            while (tcur->left != NULL) {                tlast = tcur;                tcur = tcur->left;            }            if (tcur == tlast->left) {                tlast->left = tcur->right;            }            else {                tlast->right = tcur->right;            }            cur->val = tcur->val;        }        else {            if (last == NULL) {                // only root                return NULL;            }            if (cur == last->left) {                last->left = NULL;            }            else if (cur == last->right){                last->right = NULL;            }            else {                // error            }        }        return root;    }};