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LARGEST-RECTANGLE Solution

/*
*  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 i = 0;
char ch;
while((ch = getchar()) != '\n') {
str[i++] = ch;
}
str[i] = '\0';
return i;
}

ll int arr;
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;
if(left_index == -1) {
}
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;
if(left_index == -1) {
}
else {
breadth = right_index - left_index - 1;
}

ll int area = arr[x] * breadth;
ans = MAX(ans, area);
}

printf("%lld\n", ans);

return 0;
}