#Leetcode# 515. Find Largest Value in Each Tree Row

https://leetcode.com/problems/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]

代码：

/**
 * 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> ans;
        if(!root) return ans;
        helper(root, ans, 1);
        return ans;
    }
    void helper(TreeNode* root, vector<int>& ans, int depth) {
        if(depth > ans.size()) ans.push_back(root -> val);
        else ans[depth - 1] = max(ans[depth - 1], root -> val);
        if(root -> left) helper(root -> left, ans, depth + 1);
        if(root -> right) helper(root -> right, ans, depth + 1);
    }
};

　　今天是不吃宵夜的第二天！！！今天也是被二叉树折磨得死去活来的一天