Java Program to Split an Array from Specified Position

Given an array of size N, our job is to split the array at a specific position specified by the user. Will also discuss the boundary cases.  

Consider the following example. 

From the above example let A be the original array we want to split.  Let N be the length of the array A (N = 10) and let pos be the position we want to split. In the above example pos = 5. All the elements before this position i.e; from index  0 – 4 will be split into one array while elements from index 5 – 10 are split into the later part, labeled as B and C respectively. But if the position is 0 or greater than N then it’s not able to split the array and the invalid position message is displayed.

Examples:

Input: A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0}

           pos =  5

Output:  B[] = { 1, 2, 3, 4, 5}

             C[] = { 6,7,8,9,0}

Input: A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0}

         pos = -1

Output:  Invalid position 

Input: A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0}

        pos = 20

Output:  Invalid position

Method 1: In the first method, we will be using two for loops. This approach is quite a straight forward method.

• Step 1: first we accept the value of pos from the user
• Step 2: we declare two arrays B and  C having size pos and N – pos respectively.
• Step 3: Then we have two loops the first loop runs from 0 – pos initializing array B while the second loop runs from 0 to N – pos initializing array C.

We have also added a helper method pprint() which accepts an array and prints it.  We also have an if statement checking for valid pos value.

Example:

Java

import java.util.*;

public class SplittingArray1 {

    // this method accepts a array and prints the value
    static void pprint(int arr[])
    {
        for (int var : arr) {
            System.out.print(var + " ");
        }

        System.out.println();
    }

    public static void main(String args[])
    {
        // original array
        int a[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };

        // size of array
        int n = a.length;

        // accepting the value of position from the user

        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter position to split.");

        int pos = scanner.nextInt();

        // validating the position for invalid values.
        if (pos > 0 && pos < n) {
            // method  1 : using two for loops

            // declaring array B and C
            int b[] = new int[pos];
            int c[] = new int[n - pos];

            // initializing array B
            for (int i = 0; i < pos; i++) {
                b[i] = a[i];
            }

            // initializing array C
            for (int i = 0; i < n - pos; i++) {
                c[i] = a[i + pos];
            }

            // printing the array b and c

            pprint(b);
            pprint(c);
        }

        else {
            System.out.println("Invalid position.");
        }
    }
}

Output

Enter position to split.
Invalid position.

Method 2: In this method instead of using two for loops we try to implement the same program using just one. 

• Step 1  and Step 2 are similar to method 1
• Step 3: we run a for loop from  0 to N – 1

 if index < pos 
   we initialize array B 
 else if pos >index 
   we initialize array C 

Example:

Java

import java.util.Arrays;
import java.util.Scanner;

public class SplittingArray2 {

    // this method accepts a array and prints the value
    static void pprint(int arr[])
    {
        for (int var : arr) {
            System.out.print(var + " ");
        }

        System.out.println();
    }

    public static void main(String args[])
    {

        // original array A
        int a[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };

        int n = a.length;

        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter position to split.");

        int pos = scanner.nextInt();

        if (pos > 0 && pos < n) {
            // method  2 : using only one forloop

            int b[] = new int[pos];
            int c[] = new int[n - pos];

            // only using one for loop to solve the problem.
            for (int i = 0; i < n; i++) {

                if (i < pos)
                    b[i] = a[i];
                else
                    c[i - pos] = a[i];
            }

            // printing the array b and c

            pprint(b);
            pprint(c);
        }

        else {
            System.out.println("Invalid position.");
        }
    }
}

Output

Enter position to split.
Invalid position.

Method 3: 

This is the shortest method. In this method, we use the in-built Arrays.copyOfRange() method.

public static short[] copyOfRange(short[] original, int from, int to)

original − This is the array from which a range is to be copied.

from − This is the initial index of the range to be copied, inclusive.

to − This is the final index of the range to be copied, exclusive.

Example:

Java

import java.util.Arrays;
import java.util.Scanner;

public class SplittingArray3 {

    static void pprint(int arr[])
    {
        for (int var : arr) {
            System.out.print(var + " ");
        }

        System.out.println();
    }

    public static void main(String args[])
    {
        int a[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 };

        int n = a.length;

        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter position to split.");

        int pos = scanner.nextInt();

        if (pos > 0 && pos < n) {

            // method  3 : using  Arrays.copyOfRange()

            int b[] = new int[pos];
            int c[] = new int[n - pos];

            // initializing array B by copying values from
            // index 0  to pos - 1
            b = Arrays.copyOfRange(a, 0, pos);

            // initializing array B by copying values from
            // index pos  to n - 1
            c = Arrays.copyOfRange(a, pos, n);

            // printing the array b and c

            pprint(b);
            pprint(c);
        }

        else {
            System.out.println("Invalid position.");
        }
    }
}

Output

Enter position to split.
Invalid position.

Time Complexity: O(n)

Space Complexity: O(n)