/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public int maxLevelSum(TreeNode root) {
        if(root == null) return 0;
        List<Integer> sums = new ArrayList<>();
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        while(!q.isEmpty()){
            int len = q.size();
            int sum = 0;
            while(len-->0){
                TreeNode cur = q.poll();
                sum+=cur.val;
                if(cur.left != null)
                    q.offer(cur.left);
                if(cur.right != null)
                    q.offer(cur.right);
            }
            sums.add(sum);
        }
        int ret = 0;
        int max = sums.get(0);
        for(int i=1;i<sums.size();i++){
            if(sums.get(i) > max){
                max = sums.get(i);
                ret = i+1;
            }
        }
        return ret;
    }
}