Codeforces.1334C Circle of Monsters

1.Problem
https://codeforces.com/contest/1334/problem/C

2.Idea
Only start point takes a[i] shoots, and other places a[i] - b[i-1]. Check every places as start point.

3.Source

 int n, t;  
 ll a[300005], b[300005], ac[300005];  
 void solve()  
 {  
      ll sum = 0;  
      for (int i = 0; i < n; i++) {  
           ac[i] = max(0ll, a[i] - b[(i + n - 1) % n]);  
           sum += ac[i];  
      }  
      ll ans = 1ll << 60;  
      for (int i = 0; i < n; i++) {  
           ans = min(ans, sum - ac[i] + a[i]);  
      }  
      //cout << ans << endl;  
      printf("%lld\n", ans);  
 }  
 int main()  
 {  
      scanf("%d", &t);  
      while (t--) {  
           scanf("%d", &n);  
           for (int i = 0; i < n; i++) {  
                scanf("%lld%lld", &a[i], &b[i]);  
           }  
           solve();  
      }  
      return 0;  
 }