locutus/esm/python/math/comb.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

export function comb(n, k) {
    //      discuss at: https://locutus.io/python/comb/
    // parity verified: Python 3.12
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Returns the number of ways to choose k items from n without repetition.
    //       example 1: comb(5, 2)
    //       returns 1: 10
    //       example 2: comb(10, 0)
    //       returns 2: 1
    //       example 3: comb(10, 3)
    //       returns 3: 120
    const nn = Math.trunc(Number(n));
    const kk = Math.trunc(Number(k));
    if (!Number.isFinite(nn) || !Number.isFinite(kk) || nn < 0 || kk < 0) {
        throw new Error('comb() only accepts non-negative integers');
    }
    if (kk > nn) {
        return 0;
    }
    const r = Math.min(kk, nn - kk);
    let result = 1;
    for (let i = 1; i <= r; i += 1) {
        result = (result * (nn - r + i)) / i;
    }
    return Math.trunc(result);
}