2020/day10.c


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#include <stdio.h>
#include <stdlib.h>
static int compar(const void *_a, const void *_b) {
	const int *a = _a;
	const int *b = _b;
	return *a - *b;
}
int main(void) {
	int list[256];
	int len = 0;
	while (EOF != scanf("%d\n", &list[len])) {
		len++;
	}
	list[len++] = 0;
	qsort(list, len, sizeof(int), compar);
	list[len] = list[len-1] + 3;
	len++;
	int j1 = 0, j3 = 0;
	for (int i = 1; i < len; ++i) {
		if (list[i] - list[i-1] == 1) j1++;
		if (list[i] - list[i-1] == 3) j3++;
	}
	printf("%d\n", j1 * j3);
}