The correct, optimal and working solution for programming question largest-rectangle on hackerrank

/* * Author: Arpit Bhayani * http://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; } ll int arr[100010]; stack< ll int > s; int main(int argc, char *argv[]) { int n; scanf("%d", &n); for(int i = 0 ; i < n ; i++) { scanf("%lld", &arr[i]); } int i = 0; ll int ans = 0; while(i < n) { if(s.empty() || arr[i] >= arr[s.top()]) { s.push(i); i++; } else { int x = s.top(); s.pop(); int left_index = -1; if(!s.empty()) { left_index = s.top(); } int right_index = i; int breadth = 0; if(left_index == -1) { breadth = right_index; } else { breadth = right_index - left_index - 1; } ll int area = arr[x] * breadth; ans = MAX(ans, area); } } while(!s.empty()) { int x = s.top(); s.pop(); int left_index = -1; if(!s.empty()) { left_index = s.top(); } int right_index = i; int breadth = 0; if(left_index == -1) { breadth = right_index; } else { breadth = right_index - left_index - 1; } ll int area = arr[x] * breadth; ans = MAX(ans, area); } printf("%lld\n", ans); return 0; }