LeetCode 637. Average of Levels in Binary Tree
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].
按照题目要求求解二叉树每层的平均值，既然按照层级求解，那么可以说是层次遍历或者说是BFS的典型问题。
关键在于如何正确的在遍历过程中分层，思路是根据压入队列的元素个数划分。代码如下：
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ class Solution { public: vector<double> averageOfLevels(TreeNode* root) { vector<double> v; if (root == NULL) return v; queue<TreeNode *> q; q.push(root); while (!q.empty()) { int num = q.size(); long temp = 0; for (int i = 0; i < num; i++) { TreeNode *top = q.front(); q.pop(); if (top->left != NULL) q.push(top->left); if (top->right != NULL) q.push(top->right); temp += top->val; } v.push_back((double)temp / num); } return v; } };
