Factorial/Binomial Coefficent (N Choose K) nCk=n!/(k!*(n-k)!)

gistfile1.txt

public static long factorial(int a){ //non-recursive factorial, returns long
    int answer=1; 
    for(int i=1;i<=a;i++){ //starts from 1, multiplies up, such as 1*2*3...
      answer*=i;
    }
    return(answer); 
  }
  public static long recFactorial(int a){ //recurive factorial, returns long
    if(a==1){ //stopping case for recursion: if a=1; 1!=1.
      return(1);
    }
    return(a*recFactorial(a-1)); //recursion: a!=a*(a-1)!
  }
  public static long comboChoose(int n, int k){ //combinatorics function. takes n,k
    return(factorial(n)/(factorial(k)*factorial(n-k))); //definition of nCk.
  }