Dr Wu 2 uva 2787

Loop style :
Style 1 ->
                       loop(x = 1 to N)
                          {
                               loop(y=1 to N)
                                    {
                                    }
                          }

(x,y) = 1 1 , 1 2 , 1 3, ....,2 2,......,3 3,.....N N
Style 2 ->
                       loop(x = 1 to N)
                          {
                               loop(y=x+1 to N)
                                    {
                                    }
                          }

(x,y) = 1 2 , 1 3 ,...,1 N,2 3 , 2 4 ,........ ,N-1 N  [x!=y]
If on a same list then Style 1 will include such (x,y) pairs that x==y meaning same index twice in the pair.
The second style only considers NC2 pairs meaning only 2-subsets and is useful in some problems.

Code :-

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37

using namespace std; int arr[1000]; int main() { while(true) { int idx = 1; int temp = 5; while(true) { cin>>temp; if(temp==0) break; if(temp==-1) return 0; arr[idx++] = temp; } idx--; int ans = 0; for(int x =1;x<=idx;x++) { for(int y=x+1;y<=idx;y++) { if( arr[x] == 2*arr[y] || arr[y]==2*arr[x] ) ans++; } } cout<<ans<<endl; } return 0; }