time complexity is O(n + m) where n is the first array and m is the second array. Space complexity is O(n) where n is the sizeof the map that gets created.

intersection_two_arrays.go

func intersect(nums1 []int, nums2 []int) []int {
    count := make(map[int]int)
    
    for _, n := range nums1 {
        count[n]++
    }
    
    var result []int
    for _, n := range nums2 {
        if count[n] > 0 {
            count[n]--
            result = append(result, n)
        }
    }
    
    return result
}