题目：

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代码（首刷看解析）：

class Solution {
public:
    TreeNode* deleteNode(TreeNode* root, int key) {
        if(root==nullptr){
            return nullptr;
        }
        if(root->val > key ){
            root->left = deleteNode(root->left,key);
            return root;
        }
        if(root->val < key ){
            root->right = deleteNode(root->right,key);
            return root;
        }
        if(root->val == key){
            if(root->left==nullptr && root->right == nullptr){
                return nullptr;
            }
            if(root->left==nullptr){
                return root->right;
            }
            if(root->right==nullptr){
                return root->left;
            }
            if(root->right&&root->left){
                TreeNode* successor = root->right;
                while(successor->left){
                    successor=successor->left;
                }
                root->right=deleteNode(root->right,successor->val);
                successor->right=root->right;
                successor->left=root->left;
                return successor;
            }
        }
        return root;
    }
};

代码（二刷看解析 2024年1月31日）

class Solution {
public:
    TreeNode* deleteNode(TreeNode* root, int key) {
        if (!root) return nullptr;
        
        if (root->val == key) {
            if (!root->left && !root->right){
                delete root;
                return nullptr;
            }
            else if (!root->left) {
                auto ret = root->right;
                delete root;
                return ret;
            } 
            else if (!root->right) {
                auto ret = root->left;
                delete root;
                return ret;
            }
            else{
                TreeNode* cur = root->right;
                while (cur->left) {
                    cur = cur->left;
                }
                cur->left = root->left;
                auto ret = root;
                root = root->right;
                delete ret;
                return root;
            }
        }
        if(key < root->val) root->left = deleteNode(root->left, key);
        if(key > root->val) root->right = deleteNode(root->right,key);
        return root;
    }
};