package q39

import "slices"

func mkCombs(candidates []int, target int, buf []int, ret [][]int) [][]int {
	if target == 0 {
		cp := make([]int, len(buf))
		copy(cp, buf)
		return append(ret, buf)
	}
	if len(candidates) == 0 || candidates[0] > target {
		return ret
	}
	for i := 0; candidates[0]*i <= target; i++ {
		ret = mkCombs(candidates[1:], target-i*candidates[0], buf, ret)
		buf = append(buf, candidates[0])
	}
	return ret
}

func combinationSum(candidates []int, target int) [][]int {
	slices.Sort(candidates)

	ret := make([][]int, 0, 150)
	buf := make([]int, target/candidates[0]+1)

	return mkCombs(candidates, target, buf[:0], ret)
}

var _ = combinationSum