LeetCode 637. Average of Levels in Binary Tree

^{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.

/**
 * 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;
        double ave = 0;
        queue<TreeNode*> st;
        st.push(root);
        while (!st.empty())
        {
            long long tmp = 0;
            int len = st.size();
            for (int i = 0; i < len; i++)
            {
                TreeNode *qn = st.front(); st.pop();
                if (qn->left) st.push(qn->left);
                if (qn->right) st.push(qn->right);
                tmp += qn->val;
            }
            res.push_back((double)tmp / len);            
        }
        
        return res;
    }
};