<p>Given the <code>root</code> of a binary tree, the level of its root is <code>1</code>, the level of its children is <code>2</code>, and so on.</p>

<p>Return the <strong>smallest</strong> level <code>x</code> such that the sum of all the values of nodes at level <code>x</code> is <strong>maximal</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2019/05/03/capture.JPG" style="width: 200px; height: 175px;" />
<pre>
<strong>Input:</strong> root = [1,7,0,7,-8,null,null]
<strong>Output:</strong> 2
<strong>Explanation: </strong>
Level 1 sum = 1.
Level 2 sum = 7 + 0 = 7.
Level 3 sum = 7 + -8 = -1.
So we return the level with the maximum sum which is level 2.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> root = [989,null,10250,98693,-89388,null,null,null,-32127]
<strong>Output:</strong> 2
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree is in the range <code>[1, 10<sup>4</sup>]</code>.</li>
	<li><code>-10<sup>5</sup> &lt;= Node.val &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
public:
    int maxLevelSum(TreeNode* root) {
        vector<vector<int>> answer; 
        if (root == NULL) return 0;
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            int size = q.size();
            vector<int> ans;
            for (int i = 0; i < size; i++) {
                TreeNode* front = q.front();
                q.pop();
                ans.push_back(front->val); 
                if (front->left != NULL) q.push(front->left);
                if (front->right != NULL) q.push(front->right);
            }
            answer.push_back(ans); 
        }
        int maxi = INT_MIN;
        int idx = -1;
        for (int i = 0; i < answer.size(); i++) {
            int sum = 0;
            for (int j = 0; j < answer[i].size(); j++) {
                sum += answer[i][j]; 
            }
            if( sum > maxi ){
                idx = i;
                maxi = sum;
            }  
        }

        return idx+1; 
    }
};

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