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].

 

Note:

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

以数组的形式返回每个层次上的节点的平均值

C++（19ms）：  bfs

/**
 * 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) {
        if (root == NULL)
            return vector<double>() ;
        vector<double> res ;
        queue<TreeNode*> que ;
        que.push(root) ;
        while(!que.empty()){
            long long sum = 0 ;
            int len = que.size() ;
            for(int i = 0 ; i < len ; i++){
                TreeNode* t = que.front() ;
                que.pop() ;
                sum += t->val ;
                if (t->left != NULL)
                    que.push(t->left) ;
                if (t->right != NULL)
                    que.push(t->right) ;
            }
            res.push_back(sum/(len*1.0));
        }
        return res ;
    }
};