Average of Levels in Binary Tree (E)

题目

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.

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题意

计算一个二叉树每一层值的平均值。

思路

层序遍历，注意值越界。

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代码实现

Java

class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        if (root == null) return new ArrayList<>();
        
        List<Double> ans = new ArrayList<>();
        Queue<TreeNode> q = new LinkedList<>();
        q.offer(root);
        
        while (!q.isEmpty()) {
            int size = q.size();
            long sum = 0;
            for (int i = 0; i < size; i++) {
                TreeNode cur = q.poll();
                sum += cur.val;
                if (cur.left != null) q.offer(cur.left);
                if (cur.right != null) q.offer(cur.right);
            }
            ans.add(1.0 * sum / size);
        }
        
        return ans;
    }
}