package q46

func recurse(nums []int, offset int, buf []int, seen []bool, ret [][]int) [][]int {
	if offset == len(nums) {
		a := make([]int, len(buf))
		copy(a, buf)
		return append(ret, a)
	}

	for i := range nums {
		if seen[i] {
			continue
		}
		seen[i] = true
		buf[offset] = nums[i]
		ret = recurse(nums, offset+1, buf, seen, ret)
		seen[i] = false
	}
	return ret
}

func permute(nums []int) [][]int {
	totalLen := 1
	for i := range len(nums) {
		totalLen *= i + 1
	}
	ret := make([][]int, 0, totalLen)
	buf := make([]int, len(nums))
	seen := make([]bool, len(nums))

	return recurse(nums, 0, buf, seen, ret)
}

var _ = permute