/*
 * Copyright (c) Camden Dixie O'Brien
 * SPDX-License-Identifier: AGPL-3.0-only
 */

#include "min_heap.h"

static inline int left(int i)
{
	return 2 * i + 1;
}

static inline int parent(int i)
{
	return (i - 1) / 2;
}

static inline void swap(int *xs, int a, int b)
{
	int tmp = xs[a];
	xs[a] = xs[b];
	xs[b] = tmp;
}

static void sift_down(int *xs, int root, int count)
{
	int child;
	while ((child = left(root)) < count) {
		if (child + 1 < count && xs[child] > xs[child + 1])
			++child;
		if (xs[root] > xs[child]) {
			swap(xs, root, child);
			root = child;
		} else {
			return;
		}
	}
}

void min_heap_heapify(int *xs, int count)
{
	for (int i = parent(count - 1); i >= 0; --i)
		sift_down(xs, i, count);
}

int min_heap_pop(int *xs, int *count)
{
	int min = xs[0];
	--(*count);
	xs[0] = xs[*count];
	sift_down(xs, 0, *count);
	return min;
}