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:

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

解题思路：一个简单的广度优先搜索，难点在于思考广度优先搜索每一层的个数鉴定。

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