題目描述

比較簡單的一道題目,需要注意的是要將sum的型別改成long這樣就不會溢位了，否則測試用例會出現-1這個bug：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        List<Double> list = new ArrayList<>();
		Deque<TreeNode> tem = new LinkedList<>();
		tem.offer(root);
		while (!tem.isEmpty()) {
			int size = tem.size();
			long sum = 0;
			for (int i = 0; i < size; i++) {
				TreeNode node = tem.poll();
				sum+=node.val;
				if(node.left != null){
					tem.offer(node.left);
				}
				if(node.right != null){
					tem.offer(node.right);
				}
			}
			list.add((double)sum/size);
		}
		
		return list;
    }
}