2016夏季练习——单调栈

来源：HDU1506

串的问题有毒啊

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <stack>
using namespace std;
typedef long long LL;
int n;
const int MAXN = 100000+10;
const int INF = 0x3f3f3f3f;
LL h[MAXN];
LL l[MAXN],r[MAXN];
//l,r用来找出左边右边比自己大的最远的数位置
LL ans;
int main(){
while(scanf("%d",&n)!=EOF&&n){
for(int i=1;i<=n;i++)
{
scanf("%lld",h+i);
}
l[1]=1;
r
=n;
// cout<<"start: "<<endl;
// cout<<"now it's l"<<endl;
for(int i=2;i<=n;i++){
int t=i;
while(t>1&&h[i]<=h[t-1]) t=l[t-1];//节约时间，不要直接向前推
l[i]=t;
}
// cout<<"now it's r"<<endl;
for(int i=n-1;i>=1;i--){
int t=i;
while(t<n&&h[i]<=h[t+1]) t=r[t+1];//同理
r[i]=t;
}
ans=-INF;
for(int i=1;i<=n;i++){
// cout<<"s"<<i<<"= "<<(r[i]-l[i]+1)*h[i]<<endl;
ans = max(ans,(r[i]-l[i]+1)*h[i]);
}
cout<<ans<<endl;
}
return 0;
}