156 Find Largest Value in Each Tree Row

/**
 * 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) {
        vector<int> result;
        if(!root) return result;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
          int size = q.size();
          int maxval = INT_MIN;
          while(size--){
            TreeNode* tmp = q.front();
            q.pop();
            maxval = max(tmp->val,maxval);
            if(tmp->left) q.push(tmp->left);
            if(tmp->right) q.push(tmp->right);
          }
          result.push_back(maxval);
        }
        return result;
    }
};