https://blog.csdn.net/zuzhiang/article/details/78135142
http://poj.org/problem?id=2559

my code_1 solution 1

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<stack>
using namespace std;
typedef long long ll;
ll read()
{
	char ch=' ';
	ll f=1;ll x=0;
	while(ch<'0'||ch>'9')
	{
		if(ch=='-') f=-1;ch=getchar();
	}
	while(ch>='0'&&ch<='9')
	{
	    x=x*10+ch-'0';ch=getchar();
	}
	return x*f;
}
const ll N=100100;
ll a[N];
stack <ll> s;
int main()
{
	ll n;
	ll i,j;
	while(scanf("%lld",&n)!=EOF)
	{
		if(n==0) break;
		while(!s.empty()) s.pop();
		for(i=1;i<=n;i++)
		{
			a[i]=read();
		}
		a[n+1]=-1;
		ll ans=0;
		ll top,tmp;
		for(i=1;i<=n+1;i++)
		{
			if(s.empty()||a[i]>=a[s.top()])
			{ 
				s.push(i);
			}
			else
			{
				while(!s.empty()&&a[i]<a[s.top()])
				{
					top=s.top();
					tmp=(i-top)*a[top];
					ans=max(ans,tmp);
					s.pop();
				}
				s.push(top);
				a[top]=a[i];	
			}
		}
		cout<<ans<<endl;
	}
	return 0;
}

 

my code solution 2

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<stack>
using namespace std;
typedef long long ll;
ll read()
{
	char ch=' ';
	ll f=1;ll x=0;
	while(ch<'0'||ch>'9')
	{
		if(ch=='-') f=-1;ch=getchar();
	}
	while(ch>='0'&&ch<='9')
	{
	    x=x*10+ch-'0';ch=getchar();
	}
	return x*f;
}
const ll N=100100;
ll l[N],r[N];
ll a[N];
stack <ll> s;
void init()
{
	while(!s.empty())
	{
		s.pop();
	}
}
int main()
{
	ll n;
	ll i,j;
	while(scanf("%lld",&n)!=EOF)
	{
		if(n==0) break;
		init();
		for(i=1;i<=n;i++)
		{
			a[i]=read();	
		}
		a[n+1]=-1;
		a[0]=-1;
		for(i=1;i<=n+1;i++)
		{
			if(s.empty()||a[i]>=a[s.top()])
			{
				s.push(i);
			}
			else
			{
				while(!s.empty()&&a[i]<a[s.top()])
				{
					r[s.top()]=i;
					s.pop();
				}
				s.push(i);
			}
		}
		init();
		for(i=n;i>=0;i--)
		{
			if(s.empty()||a[i]>=a[s.top()])
			{
				s.push(i);
			}
			else
			{
				while(!s.empty()&&a[i]<a[s.top()])
				{
					l[s.top()]=i;
					s.pop();
				}
				s.push(i);
			}	
		}
		ll ans=0;
		for(i=1;i<=n;i++)
		{
			ans=max((r[i]-1-l[i]-1+1)*a[i],ans);
		}
		cout<<ans<<endl;
	}
	return 0;
}