【二叉树】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   7Output: [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.

解答：

本质上还是层次遍历，不难

/** * 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> res;        queue<TreeNode*> q;        q.push(root);        while(!q.empty()){            double avg=0;            double tmp=0;            int cnt=0;            for(int i=0,n=q.size();i<n;i++){                TreeNode* p=q.front();                q.pop();                tmp+=p->val;                cnt++;                if(p->left)                    q.push(p->left);                if(p->right)                    q.push(p->right);            }            avg=tmp/cnt;            res.push_back(avg);        }        return res;    }};

一遍AC，美滋滋