如何找到一个与其他数组相交的元素

I have an array like:

a:= [1,2,3,4,5]
b:= [5,6,7,8,9]

How to know array b have contain element in array a without using foreach?

How to know array b have contain element in array a without using foreach?

You can't. And you should not try as this is pointless restriction.

If the arrays are sorted (as they appear to be in your question) there is an algorithm that works better than going through each element.

Pick the first element of a, call it x. Binary search b for the first element equal or greater than x. If they are equal, you found an element that is contained in both arrays, if not, make that your new x. Now search a for x in the same way. Repeat until you run out of elements in one of the arrays.

This can be trivially extended to an arbitrary number of arrays (in fact, it's easier to write with an arbitrary number of arrays).

Here's a quick and dirty implementation:

package main

import (
    "fmt"
    "sort"
)

func inter(arrs ...[]int) []int {
    res := []int{}
    x := arrs[0][0]
    i := 1
    for {
        off := sort.SearchInts(arrs[i], x)
        if off == len(arrs[i]) {
            // we emptied one slice, we're done.
            break
        }
        if arrs[i][off] == x {
            i++
            if i == len(arrs) {
                // x was in all the slices
                res = append(res, x)
                x++ // search for the next possible x.
                i = 0
            }
        } else {
            x = arrs[i][off]
            i = 0 // This can be done a bit more optimally.
        }
    }
    return res
}

func main() {
    a := []int{1, 2, 3, 4, 5, 7}
    b := []int{5, 6, 7, 8, 9}

    fmt.Println(inter(a, b))
}

package main

import (
    set "github.com/deckarep/golang-set"
)

func array_intersect(a, b []interface{}) []interface{} {
    return set.NewSetFromSlice(a).Intersect(set.NewSetFromSlice(b)).ToSlice()
}
func main() {
    a := []interface{}{1, 2, 3, 4, 5, 7}
    b := []interface{}{5, 6, 7, 8, 9}

    println(array_intersect(a, b))
}

package main

import (
    "fmt"
    "sort"
)

func array_intersect(a, b []int) []int {
    ret := []int{}

    lenA := len(a)
    lenB := len(b)
    if lenA == 0 || lenB == 0 {
        return ret
    }
    sort.Ints(a)
    sort.Ints(b)
    var i, j int
    for {
        a = a[i:]
        if i = sort.SearchInts(a, b[j]); i >= len(a) {
            break
        }
        if a[i] == b[j] {
            ret = append(ret, a[i])
        }
        if j++; j >= lenB {
            break
        }
    }

    return ret
}
func main() {
    a := []int{5, 7, 1, 1, 2, 3, 4, 5, 7}
    b := []int{1, 1, 5, 6, 7, 8, 9}
    fmt.Printf("a=%v, b=%v", a, b)
    fmt.Printf("%v
", array_intersect(a, b))
    fmt.Printf("a=%v, b=%v", a, b)
}