05. Average of Levels in Binary Tree.cpp

/*
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.
*/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */

class Solution
{
public:
  vector<double> averageOfLevels(TreeNode *root)
  {
    if (!root)
      return {};
    vector<double> ans;
    queue<TreeNode *> pending;
    pending.push(root);
    while (pending.size())
    {
      int size = pending.size();
      double curr_sum = 0;
      for (int i = 0; i < size; ++i)
      {
        auto curr = pending.front();
        pending.pop();
        curr_sum += curr->val;
        if (curr->left)
          pending.push(curr->left);
        if (curr->right)
          pending.push(curr->right);
      }
      ans.push_back((curr_sum * 1.0) / size);
    }

    return ans;
  }
};