solution.cpp

// level-order traversal

/**
 * 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) {}
 * };
*/
classSolution {
public:
intmaxLevelSum(TreeNode* root) {
 queue<TreeNode *> q{{root}};
int ans = INT_MIN, ans_idx = -1, idx = 1;
while(!q.empty()) {
int sz = q.size();
 vector<int> tmp;
while(sz--) {
auto t = q.front();
 q.pop();
 tmp.push_back(t->val);
if(t->left)
 q.push(t->left);
if(t->right)
 q.push(t->right);
 }
int sum = std::accumulate(begin(tmp), end(tmp), 0);
if(ans < sum) {
 ans = sum;
 ans_idx = idx;
 }
 idx++;
 }
return ans_idx;
 }
};