import "sort"

in := []int{3,2,1,4,3,2,1,4,1} // any item can be sorted
sort.Ints(in)
j := 0
for i := 1; i < len(in); i++ {
	if in[j] == in[i] {
		continue
	}
	j++
	in[i], in[j] = in[j], in[i]
}
fmt.Println(in[:j+1]) // [1 2 3 4]