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  1. #include <bits/stdc++.h>
  2. #define int long long
  3. using namespace std;
  4. const int MOD = 1e9 + 7;
  5.  
  6. int binpow(int a, int n) {
  7. 	if (n == 0) return 1;
  8. 	int x = binpow(a, n / 2);
  9. 	if (n % 2 == 0) return (x * x) % MOD;
  10. 	else return ((x * x) % MOD * a) % MOD;
  11. }
  12.  
  13. signed main() {
  14. 	ios_base::sync_with_stdio(0);
  15. 	cin.tie(0);
  16. 	int a, b;
  17. 	cin >> a >> b;
  18. 	int n = a + b - 1, k = b - 1;
  19. 	int x = 1;
  20. 	for (int i = k + 1; i <= n; ++i) x = (x * i) % MOD;
  21. 	int y = 1;
  22. 	for (int i = 1; i <= n - k; ++i) y = (y * i) % MOD;
  23. 	cout << (x * binpow(y, MOD - 2)) % MOD;
  24.     return 0;
  25. }
Success #stdin #stdout 0s 5312KB
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5 3
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21
https://ideone.com/MGNYYW
language:
C++ (gcc 8.3)
created:
1 day ago
visibility:
public

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