Golang: fill set or iteration slices

When comparing two arrays or looking for matches in them etc.
For which number of elements is it more profitable to use a map filled with all the elements of the array(time complexity O (n) ) or double iterations of arrays (time complexity O (n²))?

Implement a set in Go is to use a map with value empty structs. An empty struct doesn’t use any memory.

m := make(map[string]struct{}) //create
m["one"] = struct{}{}      //write
if val, exist := m[v1]; exist { //read
}

Read from slice is faster than map.

Use iteration slices

for _, v1 := range slice1 {
    for _, v2 := range slice2 {
        if v1 == v2 {
            cnt++
            break
        }
    }
}

Use map

for _, v := range slice2 { //fill
    m[v] = struct{}{}
}
for _, v := range slice1 { //check
    if _, exist := m[v]; exist {
        cnt++
    }
}

For a small number of elements, double iterations of arrays are faster, but for 200 elements, the times are the same.