HDU 1506 Largest Rectangle in a Histogram

 1 //#define LOCAL
 2 #include <iostream>
 3 #include <cstdio>
 4 #include <cstring>
 5 using namespace std;
 6 
 7 const int maxn = 100000 + 5;
 8 long long a[maxn], l[maxn], r[maxn];
 9 
10 int main(void)
11 {
12     #ifdef LOCAL
13         freopen("1506in.txt", "r", stdin);
14     #endif
15 
16     long long n;
17     while(scanf("%I64d", &n) == 1 && n)
18     {
19         long long ans = -1;
20         long long i, t;
21         for(i = 1; i <= n; ++i)
22             scanf("%I64d", &a[i]);
23         l[1] = 1;
24         r[n] = n;
25         for(i = 2; i <= n; ++i)
26         {
27             t = i;
28             while(t > 1 && a[i] <= a[t-1])
29                 t = l[t-1];
30             l[i] = t;
31         }
32         for(i = n-1; i > 0; --i)
33         {
34             t = i;
35             while(t < n && a[i] <= a[t+1])
36                 t = r[t+1];
37             r[i] = t;
38         }
39         long long temp;
40         for(i = 1; i <= n; ++i)
41         {
42             temp = (r[i]-l[i]+1)*a[i];
43             ans = max(ans, temp);
44         }
45         printf("%I64d\n", ans);
46     }
47     return 0;
48 }