Leetcode515. Find Largest Value in Each Tree Row在每个树行中找最大值

您需要在二叉树的每一行中找到最大的值。

示例：

输入: 1 / 3 2 / 5 3 9 输出: [1, 3, 9]

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