515. Find Largest Value in Each Tree Row

/*
You need to find the largest value in each row of a binary tree.

Example:
Input: 

          1
         / \
        3   2
       / \   \  
      5   3   9 

Output: [1, 3, 9]

*/


/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> largestValues(TreeNode* root) {
        std::vector<int> res;
        if(!root) return res;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
            int len=q.size();
            int m=INT_MIN;
            for(int i=0;i<len;i++){
                TreeNode* node=q.front();
                q.pop();
                m=max(m,node->val);
                if(node->left) q.push(node->left);
                if(node->right) q.push(node->right);
            }
            res.push_back(m);
        }
        return res;
    }
};