5kyu-josephus-survivor.js

// In this kata you have to correctly return who is the "survivor", ie: the last element of a Josephus permutation.

// Basically you have to assume that n people are put into a circle and that they are eliminated in steps of k elements, like this:

// josephus_survivor(7,3) => means 7 people in a circle;
// one every 3 is eliminated until one remains
// [1,2,3,4,5,6,7] - initial sequence
// [1,2,4,5,6,7] => 3 is counted out
// [1,2,4,5,7] => 6 is counted out
// [1,4,5,7] => 2 is counted out
// [1,4,5] => 7 is counted out
// [1,4] => 5 is counted out
// [4] => 1 counted out, 4 is the last element - the survivor!

// The above link about the "base" kata description will give you a more thorough insight about the origin of this kind of permutation, but basically that's all that there is to know to solve this kata.

// Notes and tips: using the solution to the other kata to check your function may be helpful, but as much larger numbers will be used, using an array/list to compute the number of the survivor may be too slow; you may assume that both n and k will always be >=1.

function josephusSurvivor(n, k) {
    let i = 0;
    let arr = Array.from(Array(n), (x, index) => index + 1);
    while (arr.length > 1) {
        i = (i + k - 1) % arr.length;
        arr.splice(i, 1);
    }
    return arr[0]
}