public class MinIntHeap
{
	private static int _capacity = 10;
	private int _currentSize = 0;
	private int[] _items = new int[_capacity];

	public int Peek()
	{
		if (_currentSize == 0) throw new Exception();

		return _items[0];
	}

	public int Pop()
	{
		if (_currentSize == 0) throw new Exception();

		int item = _items[0];
		_items[0] = _items[_currentSize - 1];
		_items[_currentSize - 1] = 0;
		_currentSize--;
		HeapifyDown();
		return item;
	}

	public void Insert(int item)
	{
		EnsureExtraCapacity();
		_items[_currentSize] = item;
		_currentSize++;
		HeapifyUp();
	}

	private void HeapifyUp()
	{
		var index = _currentSize - 1;
		while (HasParent(index) && Parent(index) > _items[index])
		{
			Swap(GetParentIndex(index), index);
			index = GetParentIndex(index);
		}
	}

	private void HeapifyDown()
	{
		var index = 0;
		while (HasLeftChild(index))
		{
			var smallerChildIndex = GetLeftChildIndex(index);
			if (HasRightChild(index) && RightChild(index) < LeftChild(index))
			{
				smallerChildIndex = GetRightChildIndex(index);
			}

			if (_items[index] < _items[smallerChildIndex])
			{
				break;
			}
			else
			{
				Swap(smallerChildIndex, index);
				index = smallerChildIndex;
			}
		}
	}

	private void Swap(int indexOne, int indexTwo)
	{
		int temp = _items[indexOne];
		_items[indexOne] = _items[indexTwo];
		_items[indexTwo] = temp;
	}

	private void EnsureExtraCapacity()
	{
		if (_currentSize == _capacity)
		{
			Array.Resize(ref _items, _capacity * 2);
			_capacity *= 2;
		}
	}

	private int GetLeftChildIndex(int parentIndex) => 2 * parentIndex + 1;
	private int GetRightChildIndex(int parentIndex) => 2 * parentIndex + 2;
	private int GetParentIndex(int childIndex) => (childIndex - 1) / 2;

	private bool HasLeftChild(int index) => GetLeftChildIndex(index) < _currentSize;
	private bool HasRightChild(int index) => GetRightChildIndex(index) < _currentSize;
	private bool HasParent(int index) => GetParentIndex(index) >= 0;

	private int LeftChild(int index) => _items[GetLeftChildIndex(index)];
	private int RightChild(int index) => _items[GetRightChildIndex(index)];
	private int Parent(int index) => _items[GetParentIndex(index)];
}