Golang从所有数组中存在的值创建数组

Question

I need to create an array from multiple arrays. The new array must only contain the values that is present in all arrays passed in. For example.

array1 := []string{"hello", "germany", "brasil", "fiji"}
array2 := []string{"goodbye", "germany", "brasil", "fiji"}
array3 := []string{"hello", "brasil", "fiji"}
array4 := []string{"hello", "brasil", "fiji", "usa"}

func mergeArrays(arrs ...[]string) []string{
   // process arrays
}

myNewArray := mergeArrays(array1,array2,array3,array4)
fmt.Println(myNewArray) // ["fiji", "brasil"]

The example should return ["fiji", "brasil"] since they are the only values present in all arrays.

How could I go about writing a function that could achieve such a goal in golang?

This is my attempt but feels a bit clumsy

func mergeArrays(arrs ...[]string) []string {
    var finalArr []string
    if len(arrs) == 0 {
        return finalArr
    }

    for i, a := range arrs {
        if i == 0 {
            finalArr = arrs[0]
            continue
        }
        for i, e := range finalArr {
            if !strContains(a, e) {
                finalArr = append(finalArr[:i], finalArr[i+1:]...)
            }
        }

    }

    return finalArr
}

func strContains(s []string, e string) bool {
    for _, a := range s {
        if a == e {
            return true
        }
    }
    return false
}

Playground link: https://play.golang.org/p/KRygw7OVBbn

Answer 1

Per my comment above, here's one way to do it with go maps and thus avoid iterating over potentially large slices:

func itemize(a []string) map[string]struct{} {
    m := make(map[string]struct{})
    for _, v:=range a {
        m[v] = struct{}{} // struct{}{} == an empty struct (i.e. a value that incurs no storage)
    }
    return m
}

func commonElements(arrs ...[]string) (results []string) {
    if len(arrs) == 0 {
        return // edge case
    }

    mm := itemize(arrs[0]) // master map

    for i:=1; i<len(arrs);i++ {
        m := itemize(arrs[i]) // current map
        for k := range mm {
            if _, ok := m[k]; !ok {
                delete(mm, k) // master item not in current slice, so remove from master
            }
        }
    }

    results = make([]string, len(mm)) // make a precisely sized slice...
    i:=0
    for k := range mm {
        results[i] = k // so we can insert results directly into it without using append
        i++ 
    }

    return
}

https://play.golang.org/p/pTaXR-nY9zm