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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. typedef long long int ll;
  4. const int md = 1e9+7;
  5. const int N =  100005;
  6. int fact[N],ifact[N];
  7.  
  8. int power(int a,int b)
  9. {
  10. 	int ans = 1;
  11. 	while(b)
  12. 	{
  13. 		if(b&1)
  14. 			ans=((ll)ans*a)%md;
  15. 		a = ((ll)a*a)%md;
  16. 		b>>=1;
  17. 	}
  18. 	return ans;
  19. }
  20. int nCr(int n,int k)
  21. {
  22. 	if(n<k || k<0)
  23. 		return 0;
  24. 	int ans = fact[n];
  25. 	ans = ((ll)ans*ifact[n-k])%md;
  26. 	ans = ((ll)ans*ifact[k])%md;
  27. 	return ans;
  28. }
  29. signed main()
  30. {
  31. 	//clock_t clk = clock();
  32. 	fact[0] = 1;
  33. 	ifact[0] = 1;
  34. 	for(int i=1;i<N;i++)
  35. 	{
  36. 		fact[i] = ((ll)fact[i-1]*i)%md;
  37. 	}
  38. 	ifact[N-1] = power(fact[N-1],md-2);
  39. 	for(int i = N-2;i>=0;i--)
  40. 		ifact[i] = ((ll)ifact[i+1]*(i+1))%md;
  41. 	int t;
  42. 	scanf("%d",&t);
  43. 	assert(t<=20 && t>=1);
  44. 	while(t--)
  45. 	{
  46. 	int n,k;
  47. 	scanf("%d %d",&n,&k);
  48. 	assert(n>=1 && n<=100000);
  49. 	assert(k>=0 && k<=100000);
  50. 	n>>=1;
  51. 	int ans = 0;
  52. 	for(int i=0;i<=min(n/2,k);i++)
  53. 	{
  54. 		int val = (nCr(n,i)-nCr(n,i-1))%md;
  55. 		ans = (ans + ((ll)val*val)%md)%md;
  56. 	}
  57. 	ans = ((ll)ans*power(nCr(2*n,n),md-2))%md;
  58. 	ans = ((ll)ans*(n+1))%md;
  59. 	printf("%d\n",ans);
  60. 	}
  61. 	//cout<<(float)(clock()-clk)/CLOCKS_PER_SEC;
  62. 	return 0;
  63. }
Runtime error #stdin #stdout #stderr 0s 4484KB
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Standard input is empty
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Standard output is empty
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prog: prog.cpp:43: int main(): Assertion `t<=20 && t>=1' failed.
https://ideone.com/EEMmbm
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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