637. Average of Levels in Binary Tree

Question

LeetCode Problem

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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.
Example 1:

Input: root = [3,9,20,null,null,15,7] Output: [3.00000,14.50000,11.00000]
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].

Example 2:

Input: root = [3,9,20,15,7] Output: [3.00000,14.50000,11.00000]

Constraints:

• The number of nodes in the tree is in the range [1, 10 4 ] .
• -2 31 <= Node.val <= 2 31 - 1

Solutions

Use BFS + queue

vector<double> averageOfLevels(TreeNode* root) {
	vector<double> v;
	if (!root) return v;
	queue<TreeNode*> q;
	q.push(root);
	while (!q.empty()) {
		size_t levelNum = q.size();
		double sum = 0;
		for (int i = 0; i < levelNum; ++i) {
			TreeNode* node = q.front();
			q.pop();
			sum += static_case<double>(node->val);
			if (node->left) q.push(node->left);
			if (node->right) q.push(node->right);
		}
		v.push_back(sum / levelNum);
	}
	return v;
}