Combination

combination.go

func loop(v []int, r func([]int)) {
	var i, j, n uint
	n = uint(len(v))
	a := make([]int, 0, len(v))

	for ; i < (1 << n); i++ {
		a = a[:0]
		for j = 0; j < n; j++ {
			if i&(1<<j) != 0 {
				a = append(a, v[j])
			}
		}
		r(a)
	}
}

func recursion(v []int, rcv func([]int)) {
	var rec func(a, b []int)
	rec = func(a, b []int) {
		if len(b) == 0 {
			rcv(a)
		} else {
			rec(append(a, b[0]), b[1:])
			rec(a, b[1:])
		}
	}
	a := make([]int, 0, len(v))
	rec(a, v)
}