[LeetCode] Problem 637 - Average of Levels in Binary Tree

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

Example

Input:

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2
3
4
5
  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.

Code

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public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}
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public List<Double> averageOfLevels(TreeNode root) {
    List<Double> result = new ArrayList<>();

    if (root == null)
        return result;

    Queue<TreeNode> queue = new LinkedList<>();
    queue.offer(root);

    while (!queue.isEmpty()) {
        int size = queue.size();
        long sum = 0;

        for (int i = 0; i < size; i++) {
            TreeNode node = queue.poll();
            sum += node.val;

            if (node.left != null)
                queue.offer(node.left);
            if (node.right != null)
                queue.offer(node.right);
        }

        result.add(sum * 1.0 / size);
    }

    return result;
}