623.cpp

#include<iostream>
using namespace std;

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(root==nullptr){
            return nullptr;
        }
        if(depth==1){
            return new TreeNode(val,root,nullptr);
        }
        if(depth==2){
            root->left= new TreeNode(val,root->left,nullptr);
            root->right= new TreeNode(val,nullptr,root->right);
        }else{
            root->left=addOneRow(root->left,val,depth-1);
            root->right=addOneRow(root->right,val,depth-1);
        }
        return root;
    }
};

int main(){

    return 0;
}