The correct, optimal and working solution for programming question divisible-sum-pairs on hackerrank

/* * Author: Arpit Bhayani * https://arpitbhayani.me */ #include <cmath> #include <cstdio> #include <cstdlib> #include <climits> #include <deque> #include <iostream> #include <list> #include <limits> #include <map> #include <queue> #include <set> #include <stack> #include <vector> #define ll long long #define MIN(a, b) a < b ? a : b #define MAX(a, b) a > b ? a : b using namespace std; int readline(char *str) { int i = 0; char ch; while((ch = getchar()) != '\n') { str[i++] = ch; } str[i] = '\0'; return i; } int arr[101]; int main(int argc, char *argv[]) { int n, k; scanf("%d%d", &n, &k); for(int i = 0 ; i < n ; i++) { scanf("%d", &arr[i]); } int count = 0; for(int j = 0 ; j < n ; j++) { for(int i = 0 ; i < j; i++) { if((arr[i] + arr[j]) % k == 0) { count++; } } } printf("%d\n", count); return 0; }