<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>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int maxLevelSum(TreeNode* root) {
        if(root == nullptr)
            return -1;
        vector<vector<int>> lvl;
        vector<int> temp;
        TreeNode *t;
        queue<TreeNode*> qu;
        int l;
        qu.push(root);
        while(!qu.empty())
        {
            l = qu.size();
            temp = {};
            for(int i=0;i<l;++i)
            {
                t = qu.front();
                qu.pop();
                if(t->left)
                {
                    qu.push(t->left);
                }
                if(t->right)
                {
                    qu.push(t->right);
                }
                temp.push_back(t->val);
            }
            lvl.push_back(temp);
        }
        int max_sum = root->val;
        int cur_sum;
        int max_idx=1;
        for(int i=0;i<lvl.size();++i)
        {
            cur_sum = std::accumulate(lvl[i].begin(),lvl[i].end(),0);
            if(cur_sum > max_sum)
            {
                max_sum = cur_sum;
                max_idx = i+1;
            }
        }
        return max_idx;
        
    }
};
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