Average of Levels in Binary Tree

Problem

Given the root of a binary tree, return the average value of the nodes on each level in the form of an array. Answers within 10-5 of the actual answer will be accepted.

Constraints

• The number of nodes in the tree is in the range [1, 104].
• -231 <= Node.val <= 231 - 1

Solution

The problem Average of Levels in Binary Tree can be solved by calculating the average of each nodes on the same level by implementing a breadth-first search with a queue.

Implementation

/**
 * 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)
    {
        queue<TreeNode *> nodes;
        nodes.push(root);

        vector<double> ret;

        int len;
        while ((len = nodes.size()))
        {
            double sum = 0;
            for (int i = 0; i < len; i++)
            {
                TreeNode *node = nodes.front();
                nodes.pop();

                sum += node->val;
                if (node->left != NULL)
                    nodes.push(node->left);
                if (node->right != NULL)
                    nodes.push(node->right);
            }
            ret.push_back(sum / len);
        }

        return ret;
    }
};