The correct, optimal and working solution for programming question SPALNUM on codechef

/* * 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 using namespace std; int array[100010]; int is_palin(int n) { int y = n; int x = 0; while(n) { int t = n % 10; x = x * 10 + t; n = n / 10; } return y == x; } int main(int argc, char *argv[]) { int t; for(int i = 1; i <= 100001; i++ ) { array[i] = is_palin(i); } scanf("%d", &t); while( t-- ) { int l, r; ll int answer = 0; scanf("%d%d", &l, &r); for(int i = l; i <= r ; i++) { if(array[i]) { answer += (ll int)(i); } } printf("%lld\n", answer); } return 0; }