POJ.3045 Cow Acrobats

1.Problem
http://poj.org/problem?id=3045

2.Idea
Greedy approach is accepted. Order the cows in (W_i + S_i).

3.Source

 int N;  
 struct Test {  
      ll w, s;  
      bool operator < (const Test &a)const {  
           return w + s < a.w + a.s;  
      }  
 } Tests[50004];  
 int main()  
 {  
      cin >> N;  
      for (int i = 0; i < N; i++) scanf("%d%d", &Tests[i].w, &Tests[i].s);  
      sort(Tests, Tests + N);  
      ll ans = -123456789;  
      ll cum = 0;  
      for (int i = 0; i < N; i++) {  
           ll tmp = cum - Tests[i].s;  
           cum += Tests[i].w;  
           ans = max(ans, tmp);  
      }  
      cout << ans << endl;  
      return 0;  
 }