Find Subarray Existence Using Two Pointer Approach in Go

In this Golang article, we are going to find if a given subarray exists in a given array using two pointer approach with iterative and optimized-iterative method. An array is a collection of elements of the same data type, arranged in a contiguous block of memory, and accessed using an index or a subscript.

Syntax

func isSubarrayPresent(arr []int, sub []int) bool {?}

The isSubarrayPresent() function is used to find if a given subarray exists in a given array using two pointer approach. It takes array and sub-array as its argument.

Algorithm

• Step 1 ? First, we need to import the fmt package.

• Step 2 ? Now, create an isSubarrayPresent() function that takes an array and a subarray of type integer. This function will return a boolean value indicating if sub-array is present in array or not.

• Step 3 ?

  For example 1 ?

  If the length of the sub-array is zero that means it is empty and present in any array. So, true is returned in such case. Otherwise, use for loop to match the elements of the sub-array with the array using certain conditions. And if all the elements of the sub-array are present in array then, return true else false.

  For example 2 ?

  It first checks if the length of sub-array is greater than the length of array, and if it so then it returns false. Otherwise, use for loop with if-else conditions to match the elements of the sub-array with the array using certain conditions. If there is a match, the function increments j to move on to the next element of sub-array. If there is no match, the function resets j to zero and increments i to move on to the next element of array. And if all the elements of the sub-array are present in array then, return true else false

• Step 4 ? Start the main() function. Inside the main() function, initialize the array and sub-arrays.

• Step 5 ? Now, calls the isSubarrayPresent() function and pass the array and sub-arrays to it.

• Step 6 ? Further, the resultant boolean value is printed using the fmt.Println() function.

Example 1

In this example, we will define a isSubarrayPresent() function using iterative approach that is used to find if a given subarray exists in a given array using two pointer approach.

package main

import "fmt"

func isSubarrayPresent(arr []int, sub []int) bool {
   if len(sub) == 0 {
      return true
   }

   i := 0
   j := 0

   for i < len(arr) {
      if arr[i] == sub[j] {
         j++
         if j == len(sub) {
            return true
         }
      } else {
         i -= j
         j = 0
      }
      i++
   }
   return false
}

func main() {
   arr := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
   sub1 := []int{2, 3, 4}
   sub2 := []int{4, 3, 2}
   sub3 := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

   fmt.Println(isSubarrayPresent(arr, sub1)) 
   fmt.Println(isSubarrayPresent(arr, sub2)) 
   fmt.Println(isSubarrayPresent(arr, sub3)) 
}

Output

true
false
false

Example 2

In this example, we will define a isSubarrayPresent() function using iterative approach in optimized manner that is used to find if a given subarray exists in a given array using two pointer approach.

package main

import "fmt"

func isSubarrayPresent(arr []int, sub []int) bool {
   n := len(arr)
   m := len(sub)

   if m > n {
      return false
   }

   i := 0
   j := 0

   for i < n && j < m {
      if arr[i] == sub[j] {
         j++
      } else if j > 0 && arr[i] == sub[j-1] {
         j--
         continue
      } else {
         i = i - j
         j = 0
      }
      i++
   }
   return j == m
}

func main() {
   arr := []int{10, 20, 30, 40, 50, 60, 70, 80, 90}
   s1 := []int{40, 50, 9}
   s2 := []int{5, 2, 10}
   s3 := []int{10, 20, 30, 40, 50}
   fmt.Println(isSubarrayPresent(arr, s1))
   fmt.Println(isSubarrayPresent(arr, s2))
   fmt.Println(isSubarrayPresent(arr, s3))
}

Output

false
false
true

Conclusion

We have successfully compiled and executed a go language program to find if a given subarray exists in a given array using two pointer approach along with two examples. In the first example, we have used the iterative method and in the second example, we have used the optimized-iterative method.