Average of Levels in Binary Tree

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Input:3/ \9  20/  \15   7
Output: [3, 14.5, 11]
Explanation:
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

思路：就是一个level order traverse；

/*** 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<Double>();if(root == null) {return list;}Queue<TreeNode> queue = new LinkedList<TreeNode>();queue.offer(root);while(!queue.isEmpty()) {int size = queue.size();int levelsize = size;double cursum = 0.0;while(size > 0) {TreeNode node = queue.poll();size--;cursum += node.val;if(node.left != null) {queue.offer(node.left);}if(node.right != null) {queue.offer(node.right);}}list.add(cursum / levelsize);}return list;}
}

 

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