51nod 1050 循环数组最大子段和

 1 #include<iostream>
 2 #include<algorithm>
 3 #include<cstring>
 4 #include<cstdio>
 5 #include<vector>
 6 #include<stack>
 7 #include<queue>
 8 #include<cmath>
 9 #include<map>
10 using namespace std;
11 
12 typedef long long LL;
13 const int maxn=50000+5;
14 
15 int n;
16 LL a[maxn];
17 LL d[maxn];
18 
19 int main()
20 {
21     //freopen("D:\\input.txt","r",stdin);
22     while(~scanf("%d",&n))
23     {
24         LL sum=0;
25         for(int i=1;i<=n;i++)
26         {
27             scanf("%lld",&a[i]);
28             sum+=a[i];
29         }
30         LL MAX=0,MIN=0x3f3f3f3f;
31         d[0]=0;
32         for(int i=1;i<=n;i++)
33         {
34             d[i]=max(a[i],d[i-1]+a[i]);
35             MAX=max(MAX,d[i]);
36         }
37         d[0]=0;
38         for(int i=0;i<=n;i++)
39         {
40             d[i]=min(a[i],d[i-1]+a[i]);
41             MIN=min(MIN,d[i]);
42         }
43         printf("%lld\n",max(MAX,sum-MIN));
44     }
45     return 0;
46 }