Force buckle 515 Find the maximum value in each tree row

Given the root node of a binary tree  root , Please find the maximum value of each layer in the binary tree .

Example 1：

Input : root = [1,3,2,5,3,null,9]
Output : [1,3,9]
Example 2：

Input : root = [1,2,3]
Output : [1,3]
 

Tips ：

The range of the number of nodes in a binary tree is [0,104]
-231 <= Node.val <= 231 - 1

source ： Power button （LeetCode）
link ：https://leetcode.cn/problems/find-largest-value-in-each-tree-row

Ideas ： A simple sequence traversal

/**
 * 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) {
        queue<TreeNode*> q;
        vector<int> ans;
        int mx;

        if(root!=NULL)  q.push(root);

        while(q.size()){
            int len = q.size();// Get the length of the current layer 
            TreeNode *t = q.front();
            mx=t->val;
            for(int i=0;i<len;i++){
                mx=max(t->val,mx);
                if(t->left) q.push(t->left);// Judge whether there are left children 
                if(t->right) q.push(t->right);// Judge whether there is a right child 

                q.pop();
                t=q.front();
            }
            ans.push_back(mx);
        }
        return ans;
    }
};