Going through some of the codes for certain problems I have noticed something like **invfact**. I don’t know what it means but it is used in cases where we need to calculate nPr or nCr, that too real quick. Can somebody please explain me what is the use of invfact?

Here is a piece of code for example:

```
void init(){
For(i,MaxN-1){
For(j,MaxN-1){
gcd[i+1][j+1]=__gcd(i+1,j+1);
ncr[i][j]=0;
}
}
For(i,MaxN-1) {ncr[i+1][0]=1; ncr[i+1][i+1]=1;}
fact[0]=1;
fact[1]=1;
for (int i=2;i<MaxN;i++){
fact[i]=(fact[i-1]*i)%mod;
}
invfact[MaxN-1]=fastexpo(fact[MaxN-1],mod-2);
invfact[0]=1;
for (int i=MaxN-2;i>0;i--){
invfact[i]=(invfact[i+1]*(i+1))%mod;
}
}
```

**Credits**:CodeChef: Practical coding for everyone

Another thing, in general how can we or what is the best way to precompute values of nPr and nCr?