hdu 1506 Largest Rectangle in a Histogram

#include<iostream>
#include<vector>
#include<algorithm>
#include<cstdio>
#include<queue>
#include<stack>
#include<string>
#include<map>
#include<set>
#include<cmath>
#include<cassert>
#include<cstring>
#include<iomanip>
using namespace std;

#ifdef _WIN32
#define i64 __int64
#define out64 "%I64d\n"
#define in64 "%I64d"
#else
#define i64 long long
#define out64 "%lld\n"
#define in64 "%lld"
#endif
/************ for topcoder by zz1215 *******************/
#define FOR(i,a,b)      for( int i = (a) ; i <= (b) ; i ++)
#define FFF(i,a)        for( int i = 0 ; i < (a) ; i ++)
#define FFD(i,a,b)      for( int i = (a) ; i >= (b) ; i --)
#define S64(a)          scanf(in64,&a)
#define SS(a)           scanf("%d",&a)
#define LL(a)           ((a)<<1)
#define RR(a)           (((a)<<1)+1)
#define pb              push_back
#define CL(Q)           while(!Q.empty())Q.pop()
#define MM(name,what)   memset(name,what,sizeof(name))
#define MAX(a,b)        ((a)>(b)?(a):(b))
#define MIN(a,b)        ((a)<(b)?(a):(b))
#define read            freopen("in.txt","r",stdin)
#define write           freopen("out.txt","w",stdout)

const int inf = 0x3f3f3f3f;
const i64 inf64 = 0x3f3f3f3f3f3f3f3fLL;
const double oo = 10e9;
const double eps = 10e-9;
const double pi = acos(-1.0);
const int maxn = 1000111;

int n;
i64 a[maxn];
i64 l[maxn];
int pos[maxn];
int cnt;
i64 ans;

void gao(int now,int x)
{
    while(a[cnt-1]>now)
	{
		ans=MAX(ans,(x-l[cnt-1])*a[cnt-1]);
		cnt--;
	}
	l[cnt]=pos[cnt-1]+1;
	a[cnt]=now;
	pos[cnt]=x;
	cnt++;
	return ;
}

int main()
{
	int now;
	while(cin>>n)
	{
		if(!n) return 0;
		pos[0]=l[0]=ans=0;
		a[0]=-1;
		cnt=1;
		for(int i=1;i<=n;i++)
		{
			SS(now);
			gao(now,i);
		}
		gao(-1,n+1);
		printf("%I64d\n",ans);
	}
	return 0;
}