/**
* 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) {
//建立结果数组
List<Double> ans = new ArrayList<>();
//建立队列
Queue<TreeNode> q = new LinkedList<>();
if(root == null){
return ans;
}
//将根节点放入队列
q.add(root);
//当队列非空时
while(!q.isEmpty()){
//建立临时队列用来放孩子节点
Queue<TreeNode> tem = new LinkedList<>();
long sum = 0;
int count = 0;//用来统计每层节点个数
while(!q.isEmpty()){
TreeNode cur = q.remove();
sum = sum + cur.val;
count++;
if(cur.left != null){
tem.add(cur.left);
}
if(cur.right != null){
tem.add(cur.right);
}
}
q = tem;
ans.add(sum*1.0/count);
}
return ans;
}
}
