2020/day15.c


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#include <stdio.h>
#include <stdlib.h>
int main(void) {
	int nums[2048];
	int len = 0;
	while (0 < scanf("%d,", &nums[len])) {
		len++;
	}
	while (len < 2020) {
		int last = nums[len-1];
		int next = 0;
		for (int i = len - 2; i >= 0; --i) {
			if (nums[i] == last) {
				next = len - 1 - i;
				break;
			}
		}
		nums[len++] = next;
	}
	printf("%d\n", nums[len-1]);
}