Tuesday, October 18, 2016

Reverse an array or String in java

Question:

Write a program to reverse an array or string?.

Solution:(Recursively)

1) Initialize start and end indexes
start = 0, end = n-1
2) Swap arr[start] with arr[end]
3) Recursively call reverse for rest of the array.

Sample Code:

/**
 * @author Abhinaw.Tripathi
 *
 */
public class ReverseArray
{
public static void reverse(int arr[],int start,int end)
{
int temp;
if(start>=end)
return;

temp=arr[start];
arr[start]=arr[end];
arr[end]=temp;
reverse(arr, start+1, end-1);
}

public static void printArray(int arr[], int size)
{
       for (int i=0; i < size; i++)
           System.out.print(arr[i] + " ");
       System.out.println("");
}

public static void main(String[] args)
{
    int arr[] = {1, 2, 3, 4, 5, 6};
            printArray(arr, 6);
            reverse(arr, 0, 5);
           System.out.println("Reversed array is ");
           printArray(arr, 6);
}
}


Output:

1 2 3 4 5 6
Reversed array is
6 5 4 3 2 1

Time Complexity: O(n)

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