（Java）leetcode-637 Average of Levels in Binary Tree (二叉树的层平均值)

r囧r小猫 2023-02-16 01:46 120阅读 0赞

# 题目描述 #

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

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# 思路 #

采用层序遍历，参考[leetcode-559][]。  
采用**队列**，当同一层节点全部出队后计算平均值。  
注意求和要使用double类型的变量来记录。

## 代码 ##

class Solution { 
        public List<Double> averageOfLevels(TreeNode root) { 
            List<Double> list = new ArrayList<>();
            if (root == null) return list;
            Queue<TreeNode> queue = new LinkedList<>();
            queue.offer(root);
            while(!queue.isEmpty()) { 
            	int size = queue.size();
            	double levelSum = 0.0; 
            	// 将同一层的全部出队
            	for(int i =0; i < size; i++) { 
            		TreeNode current = queue.poll();
            		levelSum += current.val;
            	    if(current.left != null) queue.offer(current.left);
            	    if(current.right != null) queue.offer(current.right);
            	}
            	list.add(levelSum / size);
            }
            return list;
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3o3MTQ0MDU0ODk_size_16_color_FFFFFF_t_70 1]

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[leetcode-559]: https://blog.csdn.net/z714405489/article/details/106495173
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3o3MTQ0MDU0ODk_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200607114220950.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3o3MTQ0MDU0ODk=,size_16,color_FFFFFF,t_70