Created
June 10, 2021 13:10
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>> ncr % m | |
>>> Resources: | |
T-1 : https://cp-algorithms.com/combinatorics/binomial-coefficients.html | |
T-2 : https://www.geeksforgeeks.org/multiplicative-inverse-under-modulo-m/ | |
>>> Implementation | |
ll fact[N], facti[N]; | |
ll be(ll a,ll b) | |
{ | |
if(b==0) | |
{ | |
return 1; | |
} | |
if(b==1) | |
{ | |
ll ans=a%M; | |
return ans; | |
} | |
if(b%2==0) | |
{ | |
a=a%M; | |
a=(a*a)%M; | |
ll ans=be(a,b/2)%M; | |
return ans; | |
} | |
else | |
{ | |
a=a%M; | |
ll val=a; | |
a=(a*a)%M; | |
ll ans=be(a,b/2)%M; | |
ans=(val*ans)%M; | |
return ans; | |
} | |
} | |
ll factinv(ll val) | |
{ | |
/* Modulo Property (a)^-1 = ((a)^(m-2))% m */ | |
/* Only If m is a prime */ | |
return be(val, M-2); | |
} | |
void factorialinv() | |
{ | |
facti[N-1]=factinv(fact[N-1]); | |
for(ll i=N-2;i>=0;i--) | |
{ | |
facti[i]=facti[i+1]*(i+1); | |
facti[i]%=M; | |
} | |
} | |
void factorial() | |
{ | |
fact[0]=fact[1]=1; | |
for(ll i=2;i<N;i++) | |
{ | |
fact[i]=fact[i-1]*i; | |
fact[i]%=M; | |
} | |
factorialinv(); | |
} | |
ll pnc(ll x,ll y) | |
{ | |
if(y>x) | |
{ | |
return 0; | |
} | |
ll num=fact[x]; | |
num*=facti[x-y]; | |
num%=M; | |
num*=facti[y]; | |
num%=M; | |
return num; | |
} | |
>>> Problems : | |
Problem-1: https://codeforces.com/contest/1312/problem/D | |
Solution : https://codeforces.com/contest/1312/submission/87856445 | |
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