51nod1050 循环数组最大子段和

思路：

分两种情况讨论。

实现：

 #include <bits/stdc++.h>
 using namespace std;
 typedef long long ll;
 const int N = ;
 ll sum[N];
 int main()
 {
     int n, x;
     while (cin >> n)
     {
         ll maxn = , minn = , ans = , mins = ;
         for (int i = ; i <= n; i++)
         {
             cin >> x; sum[i] = sum[i - ] + x;
             ans = max(ans, sum[i] - minn);
             mins = min(mins, sum[i] - maxn);
             maxn = max(maxn, sum[i]); minn = min(minn, sum[i]);
         }
         ans = max(ans, sum[n] - mins);
         cout << ans << endl;
     }
     return ;
 }