POJ2559 Largest Rectangle in a Histogram（单调栈）

 1 #include<cstdio>
 2 #include<algorithm>
 3 using namespace std;
 4 #define MAXN 111111
 5 int a[MAXN];
 6 int l[MAXN],r[MAXN];
 7 int stack[MAXN],top;
 8 int main(){
 9     int n;
10     while(~scanf("%d",&n) && n){
11         for(int i=1; i<=n; ++i){
12             scanf("%d",a+i);
13         }
14         a[++n]=-1;
15         top=0;
16         for(int i=1; i<=n; ++i){
17             l[i]=r[i]=i;
18             while(top && a[stack[top]]>a[i]){
19                 l[i]=l[stack[top]];
20                 r[stack[top]]=i-1;
21                 --top;
22             }
23             if(top && a[stack[top]]==a[i]) l[i]=l[stack[top]];
24             stack[++top]=i;
25         }
26         long long res=0;
27         for(int i=1; i<n; ++i){
28             res=max(res,(r[i]-l[i]+1LL)*a[i]);
29         }
30         printf("%lld\n",res);
31     }
32     return 0;
33 }