hdu 1506 Largest Rectangle in a Histogram

http://acm.hdu.edu.cn/showproblem.php?pid=1506

就是对一个点向左向右知道找到高度比它低的点然后记录在左右两个数组里面，再dp处理。

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #define maxn 200000
 5 #define ll __int64
 6 using namespace std;
 7 
 8 int n;
 9 ll a[maxn];
10 ll l[maxn],r[maxn];
11 
12 int main()
13 {
14     while(scanf("%d",&n)!=EOF)
15     {
16         if(n==0) break;
17         for(int i=1; i<=n; i++)
18         {
19             scanf("%I64d",&a[i]);
20             l[i]=i;
21             r[i]=i;
22         }
23         a[0]=a[n+1]=-1;
24         for(int i=1; i<=n; i++)
25         {
26             while(a[i]<=a[l[i]-1]) l[i]=l[l[i]-1];
27         }
28         for(int i=n; i>=1; i--)
29         {
30             while(a[i]<=a[r[i]+1]) r[i]=r[r[i]+1];
31         }
32         ll max1=0;
33         for(int i=1; i<=n; i++)
34         {
35             max1=max(max1,a[i]*(r[i]-l[i]+1));
36         }
37         printf("%I64d
",max1);
38     }
39     return 0;
40 }

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