The correct, optimal and working solution for programming question consecutive-subsequences 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 main(int argc, char *argv[]) { int t; scanf("%d", &t); while(t--) { int n, k; scanf("%d%d", &n, &k); ll int * counts = (ll int *) calloc(100, sizeof(ll int)); counts[0] = 1; ll int sum = 0; for(int i = 0 ; i < n ; i++) { int x; scanf("%d", &x); sum += x; if(sum >= k) { sum %= k; } counts[sum]++; } ll int count = 0; for(int i = 0 ; i < k; i++) { count += ((counts[i] * (counts[i] - 1)) / 2); } printf("%lld\n", count); free(counts); } return 0; }