解题思路

广度优先搜索。

相关代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int maxLevelSum(TreeNode root) {
        int depth=0;
        int maxdepth=1;
        int max=Integer.MIN_VALUE;
        Queue<TreeNode> queue = new LinkedList<>();

        //处理特殊情况
        if(root==null) return maxdepth;
        //把根节点放到队列中
        queue.add(root);

        while(queue.isEmpty()==false){
            int len = queue.size();
            int sum = 0;

            for(int i=0;i<len;i++){
                TreeNode node = queue.poll();
                if(node.left!=null) queue.add(node.left);
                if(node.right!=null) queue.add(node.right);
                //储层上一层的元素
                sum=sum+node.val;
            }
            depth++;
            if(max<sum){
                maxdepth = depth;
                max = sum;
            }
        }
        return maxdepth;
    }
}