aoc1.c

#include <stdio.h>

#define INPUT_LEN 200

// Get the three numbers from a list of INPUT_LEN that sum to 2020
// and return their product
int main(){
	FILE *fp;
	int nums[INPUT_LEN];
	fp = fopen("input.txt", "r");

	int i = 0;
	while(fscanf(fp, "%d", &nums[i]) != EOF)
		++i;

  // all the nested loops
	for(int x = 0; x<INPUT_LEN-1; ++x){
		for(int y=x+1; y<INPUT_LEN; ++y){
			for(int z=0; z<INPUT_LEN; ++z){
				if(nums[x] + nums[y] + nums[z] == 2020 && z != y && x != z){
					printf("answer: %d\n", nums[x] * nums[y] * nums[z]);
				}
			}
		}
	}
	
	return 0;
}