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) {
        if(!root) return vector<int>();
        queue<TreeNode *> q;
        q.push(root);
        int current = 1;
        int next = 0;
        vector<int> ret;
        int max = INT_MIN;
        while(!q.empty())
        {
            TreeNode * node = q.front();
            q.pop();
            if(node->val > max) max = node->val;
            if(node->left)
            {
                next++;
                q.push(node->left);
            }
            if(node->right)
            {
                next++;
                q.push(node->right);
            }
            
            if(--current == 0)
            {
                current = next;
                next = 0;
                ret.push_back(max);
                max = INT_MIN;
            }
        }
        
        return ret;
    }
};