20201115.md

Algorithm

637. Average of Levels in Binary Tree

Description

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:

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

Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        List<Double> result = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        if(root==null){
            return result;
        }
        queue.add(root);
        while(!queue.isEmpty()){
            int size = queue.size();
            double sum = 0;
            for(int i=0;i<size;i++){
                TreeNode temp = queue.poll();
                sum+=temp.val;
                if(temp.left!=null){
                    queue.add(temp.left);
                }
                if(temp.right!=null){
                    queue.add(temp.right);
                }
            }
            result.add(sum/size);
        }
        return result;
    }
}

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还是考察二叉树的层次遍历

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