Java: Calculating binomial coefficient

Question

I have the following programm calculating the binomial coefficient of two integers. But I want to change the programm, that it calculates and saves only the necessary coeffi

Answer 1

Do you want to keep your code afterall? Because you can also compute the binominal coefficient recursively, which would reduce your function to these 4 lines:

static long binomi(int n, int k) {
        if ((n == k) || (k == 0))
            return 1;
        else
            return binomi(n - 1, k) + binomi(n - 1, k - 1);
    }

Answer 2

What about this Code from this site

 private static long binomial(int n, int k)
    {
        if (k>n-k)
            k=n-k;

        long b=1;
        for (int i=1, m=n; i<=k; i++, m--)
            b=b*m/i;
        return b;
    }

Answer 3

You don't say which coefficients youi need. If you need C(N,n) for some fixed N, you could translate the C code below, which uses a one dimensional array. After the call, C[n] will hold the binomial coefficient C(N,n) for 0<=m<=N, as long as N is at most 66 -- if you need bigger N you will need to use an integral type with more bits.

static  int64_t*    pascals_triangle( int N)
{
int n,k;
int64_t*    C = calloc( N+1, sizeof *C);
    for( n=0; n<=N; ++n)
    {   C[n] = 1;
        k = n;
        while( --k>0)
        {   C[k] += C[k-1];
        }
    }
    return C;
}