Create nCr.cpp

Author: manitajay

Templates/nCr.cpp

@@ -0,0 +1,41 @@
+ll fact[500005];
+ 
+ll sum(ll x,ll y){
+ return (x%mod + y%mod)%mod;
+}
+ 
+ll mul(ll x,ll y){
+ return ((x%mod)*(y%mod))%mod;
+}
+ 
+ 
+ll modInverse(ll a, ll m)
+{
+ ll m0 = m;
+ ll y = 0, x = 1;
+ 
+ if (m == 1)
+ return 0;
+ 
+ while (a > 1) {
+ ll q = a / m;
+ ll t = m;
+ m = a % m, a = t;
+ t = y;
+ y = (x - mul(q, y)+mod)%mod;
+ x = t;
+ }
+ 
+ if (x < 0)
+ x = sum(x,m0);
+ 
+ return x;
+}
+ 
+ 
+ll ncr(ll n,ll r){
+ ll ans=(fact[n]);
+ ans=mul(ans,modInverse(fact[n-r],mod));
+ ans=mul(ans,modInverse(fact[r],mod));
+ return ans;
+}