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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.
题意:计算一颗二叉树的每一层所有节点值相加所得的平均数;
解法:实际上我们需要解决的是二叉树的层次遍历问题;我们可以利用队列来实现,首先,将根节点入队;每次遍历队列中所有元素,这些元素都是这一层的所有节点,可以求得节点值得平均值,对这些节点遍历时,同时将其所有节点入队;直到最后队列为空;
Java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public List<Double> averageOfLevels(TreeNode root) {
List<Double> result = new ArrayList<>();
LinkedList<TreeNode> nodes = new LinkedList<>();
if (root == null) return result;
nodes.add(root);
while (nodes.size() > 0) {
double sum = 0L;
int len = nodes.size();
for (int i = 0; i < len; i++) {
TreeNode temp = nodes.remove();
sum += temp.val;
if (temp.left != null) nodes.add(temp.left);
if (temp.right != null) nodes.add(temp.right);
}
result.add(sum / len);
}
return result;
}
}