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;
}
static int list[256];
static int len;
static long tail[256];
static long chains(int i) {
	if (i == len - 1) tail[i] = 1;
	if (tail[i]) return tail[i];
	for (int j = i + 1; j <= i + 3 && j < len; ++j) {
		if (list[j] - list[i] <= 3) tail[i] += chains(j);
	}
	return tail[i];
}
int main(void) {
	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);
	printf("%ld\n", chains(0));
}