Go: Generate all permutations of a slice or string

// Perm calls f with each permutation of a.
func Perm(a []rune, f func([]rune)) {
	perm(a, f, 0)
}

// Permute the values at index i to len(a)-1.
func perm(a []rune, f func([]rune), i int) {
	if i > len(a) {
		f(a)
		return
	}
	perm(a, f, i+1)
	for j := i + 1; j < len(a); j++ {
		a[i], a[j] = a[j], a[i]
		perm(a, f, i+1)
		a[i], a[j] = a[j], a[i]
	}
}

Example usage:

Perm([]rune("abc"), func(a []rune) {
	fmt.Println(string(a))
})

Output:

abc
acb
bac
bca
cba
cab

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