LeetCode 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].

Note:

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

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求二叉树每一层的平均数。简单题，BFS层次遍历。代码如下： [cpp] class Solution { public: vector<double> averageOfLevels(TreeNode* root) { if (root == NULL)return{}; vector<double> ans; queue<TreeNode*> q; q.push(root); while (!q.empty()) { double sum = 0; size_t n = q.size(); for (size_t i = 0; i < n; ++i) { TreeNode* f = q.front(); q.pop(); sum += f->val; if (f->left != NULL)q.push(f->left); if (f->right != NULL)q.push(f->right); } ans.push_back(sum / n); } return ans; } }; [/cpp] 本代码提交AC，用时15MS。]]>