Binomial function. Calculates the number of ways of picking k unordered from the given number of possibilities.

binomial.js

/**
 * Calculates the number of ways of picking k unordered.
 * @params {Interger}
 * @return {Interger}
*/

function binomial(n, k) {
  if (k === 0) {
    return 1;
  } else if (2*k > n) {
    return binomial(n, n-k);
  } else {
    e = n-k + 1;
    for (i = 2; i < k +1; i++) {
      e *= (n-k + i);
      e /= i;
    }
    return e;
  }
}