How to implement intersection of arrays in Golang

There are two common methods for finding the intersection of arrays in Golang: using the built-in append function, looping to determine whether the element is in another array, and superposing to find the intersection. Use map to exclude duplicate elements and obtain intersections efficiently by creating a mapping table.

Golang array intersection implementation method

In Golang, there are several methods to solve array intersection. This article will introduce the two most common methods: using the built-in append function and using map.

Method 1: Use the built-in append function

append function can add elements to an existing array, It is also possible to create a new array. We can use this feature to find the intersection:

func intersection(a, b []int) []int {
    result := []int{}
    for _, v := range a {
        if containsInArray(b, v) {
            result = append(result, v)
        }
    }
    return result
}

func containsInArray(arr []int, elem int) bool {
    for _, v := range arr {
        if v == elem {
            return true
        }
    }
    return false
}

Method 2: Use map

Another way to find the intersection is to use map. Compared with the append function, using map is more efficient because it can exclude duplicate elements in O(n) time complexity:

func intersection(a, b []int) []int {
    m := make(map[int]bool)
    for _, v := range a {
        m[v] = true
    }

    result := []int{}
    for _, v := range b {
        if m[v] {
            result = append(result, v)
        }
    }
    return result
}

Practical case

Suppose we have the following two arrays:

a := []int{1, 2, 3, 4, 5, 6}
b := []int{3, 4, 5, 6, 7, 8}

Use the append function to find the intersection:

intersectionAB := intersection(a, b)
fmt.Println(intersectionAB) // [3 4 5 6]

Use map Find the intersection:

intersectionBA := intersection(b, a)
fmt.Println(intersectionBA) // [3 4 5 6]

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