二叉排序树删除节点

对应LeetCode
450. 删除二叉搜索树中的节点
思路：找到这个节点，并标记其父节点，根据其在树中的位置做相应的处理，以保证二叉排序树的性质，因为根节点没有父节点，所以需要特殊处理。

TreeNode* deleteNode(TreeNode* root, int key) {
        TreeNode* parent = root;
        TreeNode* cur = root;
        while(cur) {//找到这个节点，并标记它的父节点
            if (cur->val > key) {
                parent = cur;
                cur = cur->left;
            } else if (cur->val < key) {
                parent = cur;
                cur = cur->right;
            } else {
                break;
            }
        }
        if (cur != nullptr) {//节点存在
            if (cur->left == nullptr) {//左子树为空
                if (cur->right == nullptr && cur == root) {//为根节点，且左右子树为空
                    delete cur;
                    return nullptr;
                } else if(cur == parent) {//为根节点，且右子树不空
                    cur = cur->right;
                    delete parent;
                    return cur;
                } 
                else {//不是根节点
                    parent->left == cur ? parent->left = cur->right : parent->right = cur->right;
                    delete cur;
                    cur = nullptr;
                }
            } else if(cur->right == nullptr) {//右子树为空
                if (parent == cur) {//为根节点，且左子树不空
                    cur = cur->left;
                    delete parent;
                    return cur;
                }else{//不是根节点
                    parent->left == cur ? parent->left = cur->left : parent->right = cur->left;
                    delete cur;
                    cur = nullptr;
                }
                
            } else {//左右都不为空，找到其右子树最小节点/左子树最大节点代替此节点，这里用前者
                TreeNode* rightMin = cur->right;
                parent = cur->right;
                while(rightMin->left != nullptr) {
                    parent = rightMin;
                    rightMin = rightMin->left;
                }
                cur->val = rightMin->val;
                if (rightMin == parent) {
                    cur->right = rightMin->right;
                } else {
                    parent->left = rightMin->right;
                }
                delete rightMin;
                rightMin = nullptr;
            }
        }
        return root;
        
    }