This is my solution
Line number 34 return ((fact[n]*1LL*inv[r])%mod*inv[n-r])%mod; is being copied from other’s solution.
(nCr)%P is equivalent to (n! /(r! * (n-r)!))%P
// according to modular mathematics
=> (n!%P * modInverseOf(r! * (n-r)!)%P)%
// we are doing the same in the solution
// correct solution
((fact[n]*1LL*inv[r])%mod*inv[n-r])%mod;
// my incorrect solution
(fact[n]*1LL*(inv[r]*inv[n-r])%mod)%mod;
// inv[i] contains the mod inverse of i
// fact[n] contains n!%P