Heap's Permutation

package main

import "fmt"

type Heap[T any] struct {
	arr     []T
	pointer int
	stack   []int
}

func (h *Heap[T]) Next() bool {

	for {
		// if pointer reaches to end of stack, there is no new permutations to generate
		if h.pointer >= len(h.arr) {
			return false
		}

		if h.stack[h.pointer] < h.pointer {

			if h.pointer%2 == 0 {
				h.arr[0], h.arr[h.pointer] = h.arr[h.pointer], h.arr[0]
			} else {
				h.arr[h.stack[h.pointer]], h.arr[h.pointer] = h.arr[h.pointer], h.arr[h.stack[h.pointer]]
			}

			h.stack[h.pointer]++
			h.pointer = 1

			return true
		} else {

			h.stack[h.pointer] = 0
			h.pointer++

		}
	}

}

func (h *Heap[T]) Current() []T {
	return h.arr
}

func NewHeap[T any](arr []T) Heap[T] {

	s := []int{}
	for i := 0; i < len(arr); i++ {
		s = append(s, 0)
	}

	return Heap[T]{
		arr:     arr,
		pointer: 1,
		stack:   s,
	}
}

func main() {

	list := []int{1, 2, 3}

	h := NewHeap(list)

	i := 1
	for {
		fmt.Printf("%d) %d\n", i, h.Current())
		if !h.Next() {
			break
		}
		i++
	}

}