637. Average of Levels in Binary Tree
637. Average of Levels in Binary Tree
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题目
Given the root of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within 10-5 of the actual answer will be accepted.
Example 1:
Input: root = [3,9,20,null,null,15,7]
Output: [3.00000,14.50000,11.00000]
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].
Example 2:
Input: root = [3,9,20,15,7]
Output: [3.00000,14.50000,11.00000]
Constraints:
- The number of nodes in the tree is in the range
[1, 104]. -2^31 <= Node.val <= 2^31 - 1
题目大意
按层序从上到下遍历一颗树，计算每一层的平均值。
解题思路
使用一个队列进行层序遍历，每次 for 循环时计算每层元素之和，再除以每层元素的个数 len，即可得到平均数。
代码
/**
* @param {TreeNode} root
* @return {number[]}
*/
var averageOfLevels = function (root) {
let res = [];
if (!root) return res;
let queue = [root];
while (queue.length) {
let len = queue.length;
let temp = 0;
for (let i = 0; i < len; i++) {
if (queue[i].left) queue.push(queue[i].left);
if (queue[i].right) queue.push(queue[i].right);
temp += queue[i].val;
}
queue = queue.slice(len);
res.push(temp / len);
}
return res;
};