Check if a Slice Contains a Value in Go

Clive B.

—October 15, 2024

The ProblemThe Problem

You don’t know how to check whether a given value exists in a slice.

The SolutionThe Solution

In Go version 1.21 and later, you can use the slices.Contains function to check whether a slice contains a specific value.

The following example tests for the presence of the numbers 42 and 41 in the integer slice, []int{8, 21, 42}:

package main

import (
    "fmt"
    "slices"
)

func main() {
    example := []int{84, 21, 42}

    fmt.Println(slices.Contains(example, 42)) // Prints "true".
    fmt.Println(slices.Contains(example, 41)) // Prints "false".
}

Note: In the worst case, using slices.Contains has linear time complexity, meaning that it will have to check every element in the slice.

Finding a Value in a Sorted SliceFinding a Value in a Sorted Slice

If your slice has already been sorted, you can use the slices.BinarySearch function to check whether it contains a given value.

package main

import (
    "fmt"
    "slices"
)

func main() {
    example := []int{84, 21, 42}
    index, found := slices.BinarySearch(example, 42)
    fmt.Println(index, found) // Prints "2 true".
}

This is significantly faster than the Contains function, as the BinarySearch function runs in logarithmic time.

Further ReadingFurther Reading

• The Go slices package documentation