515. Find Largest Value in Each Tree Row

The first time to pass in once try, congratulate me

/** * 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:
    vector<int> largestValues(TreeNode* root) {
    
        if (!root) {
    
            return {
    };
        }
        queue<TreeNode *> q;
        vector<int> res;
        q.push(root);
        while(!q.empty()){
    
            int len = q.size();
            int max_val = INT_MIN;
            while (len){
    
                TreeNode *tmp = q.front();
                max_val = max(tmp->val, max_val);
                q.pop();
                --len;
                if (tmp->left) {
    
                    q.push(tmp->left);
                } 
                if (tmp->right) {
    
                    q.push(tmp->right);
                }
            }
            res.emplace_back(max_val);
        }
        return res;
    }
};