Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

Example 1:

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].

Note:

  1. The range of node's value is in the range of 32-bit signed integer.

按层遍历,求每层平均值。

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
import java.util.LinkedList;
import java.util.Queue;
public class Solution {
public List<Double> averageOfLevels(TreeNode root) {
List<Double> retList = new ArrayList<Double>();
if (root == null)
return retList; Queue<TreeNode> q = new LinkedList<TreeNode>();
q.offer(root); while ( ! q.isEmpty() ) {
List<TreeNode> tl = new ArrayList<TreeNode>();
double sum = 0;
while ( ! q.isEmpty() ) {
TreeNode curr = q.poll();
tl.add(curr);
sum += (double) curr.val;
}
retList.add(sum / tl.size());
for (TreeNode n : tl) {
if (n.left != null)
q.offer(n.left);
if (n.right != null)
q.offer(n.right);
}
}
return retList;
}
}
 

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