365 days challenge LeetCode1000 questions - Day 050 add a row to the binary tree binary tree

623. 在二叉树中增加一行

代码实现（自解）

/** * 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* addOneRow(TreeNode* root, int val, int depth) {
    
        if (depth == 1) return new TreeNode(val, root, NULL);
        if (!root) return root;
        if (depth == 2) {
    
            TreeNode* l = new TreeNode(val);
            TreeNode* r = new TreeNode(val);
            l->left = root->left;
            r->right = root->right;
            root->left = l;
            root->right = r;
            return root;
        }
        root->left = addOneRow(root->left, val, depth - 1);
        root->right = addOneRow(root->right, val, depth - 1);
        return root;
    }
};