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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. const int MAXN = 100000;
  4. const int mod = 1e9+7;
  5. using ll = long long;
  6. ll fact[MAXN + 1] , ifact[MAXN + 1];
  7.  
  8. ll power(ll base , ll exp){
  9. 	int res = 1;
  10. 	while(exp>0){
  11. 		if(exp%2 == 1)res = (res*base)%mod;
  12. 		base =  (base*base)%mod;
  13. 		exp/=2;
  14. 	}
  15. 	return res;
  16. }
  17.  
  18. void pre(){
  19. 	fact[0]=ifact[0]=1;
  20. 	for(int i = 1 ; i<=MAXN ;i++){
  21. 		fact[i] = (fact[i-1]*i)%mod;
  22. 	}
  23. 	ifact[MAXN] = power(fact[MAXN],mod-2);
  24. 	for(int i = MAXN - 1; i>=0 ;i--){
  25. 		ifact[i] = (ifact[i+1]*(i+1))%mod;
  26. 	}
  27. }
  28.  
  29. ll nCr(int n,int r){
  30. 	if(r>n || r<0)return 0;
  31. 	return (((fact[n]*ifact[r])%mod)*ifact[n-r])%mod;
  32. }
  33. int main() {
  34.    pre();
  35.    int t,n,r;
  36.    cin>>t;
  37.    while(t--){
  38.    	cin>>n>>r;
  39.    	cout<<nCr(n,r)<<endl;
  40.    }
  41.    return 0;
  42. }
Success #stdin #stdout 0.01s 5328KB
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https://ideone.com/N6gSJr
language:
C++ (gcc 8.3)
created:
7 hours ago
visibility:
public

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