hdu 1506 Largest Rectangle in a Histogram 构造

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<cstdlib>
 5 #include<cmath>
 6 #include<algorithm>
 7 #define inf 0x7fffffff
 8 using namespace std;
 9 typedef long long LL;
10 const int maxn=100000+10;
11 
12 int n;
13 int l[maxn],r[maxn],an[maxn];
14 
15 int main()
16 {
17     while (scanf("%d",&n)!=EOF && n)
18     {
19         for (int i=1 ;i<=n ;i++) {scanf("%d",&an[i]);l[i]=r[i]=i;}
20         an[0]=an[n+1]=-1;
21         l[0]=l[n+1]=r[0]=r[n+1]=0;
22         for (int i=1 ;i<=n ;i++)
23         {
24             while (an[l[i]-1 ]>=an[i])
25                 l[i]=l[l[i]-1 ];
26         }
27         for (int i=n ;i>=1 ;i--)
28         {
29             while (an[r[i]+1 ]>=an[i])
30                 r[i]=r[r[i]+1 ];
31         }
32         LL ans=0;
33         for (int i=1 ;i<=n ;i++)
34         {
35             LL area=(LL)(r[i]-l[i]+1)*(LL)an[i];
36             if (area>ans) ans=area;
37         }
38         printf("%I64d\n",ans);
39     }
40     return 0;
41 }