permutations.kt

fun permutations(A: IntArray): Array<IntArray> {
    var N = A.size
    var perms = mutableListOf<IntArray>()
    fun go(i: Int = 0) {
        if (i == N) {
            perms.add(A.copyOf())
            return
        }
        for (k in i until N) {
            A[i] = A[k].also{ A[k] = A[i] }
            go(i + 1)
            A[i] = A[k].also{ A[k] = A[i] }
        }
    }
    go()
    return perms.toTypedArray()
}