Average of Levels in Binary Tree

投稿日 |

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:

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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].

Note:

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

Method

先遍历整个数，将每个节点按深度放置，然后求平均值。

Solution

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<Double> averageOfLevels(TreeNode root) {
        List<Double> res = new ArrayList<Double>();
        List<List<TreeNode>> temp = new ArrayList<List<TreeNode>>();
        LevelTravel(temp, 0, root);
        for(int i = 0; i < temp.size(); i++){
            Double sum = 0.0;
            for(int j = 0; j < temp.get(i).size(); j++){
                sum += temp.get(i).get(j).val;
            }
            res.add(sum/temp.get(i).size());
        }
        return res;
        
    }
    
    public void LevelTravel(List<List<TreeNode>> temp, int level, TreeNode node){
        if(node == null) return;
        if(temp.size() < level + 1){
            temp.add(new ArrayList<TreeNode>());
        }
        temp.get(level).add(node);
        LevelTravel(temp, level+1, node.left);
        LevelTravel(temp, level+1, node.right);
    }
}