# Reverse the given Array without using built in function

Objective: Given a array, write an algorithm to reverse the array.

Example:

```int a[] = {1, 2, 3, 4, 5}
Output: {5, 4, 3, 2, 1}
```

Approach:

• It’s obvious that you cannot use any built-in function reverse it.
• It’s a simple solution, we will solve it using recursive and non-recursive way.
• Take 2 elements at a time, one from the from start and one from the end and swap them.
• Now for recursion, Make a recursive call to rest of the string and for non-recursive solution, use the for loop and swap the elements start +1 and end +1.

Code:

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 import java.util.*; public class ReverseArray { static int [] a; public static void reverseIteration(){ int start =0; int end = a.length–1; while(start<=end){ int temp = a[start]; a[start] = a[end]; a[end] = temp; start++; end—; } } public static void reverseRecursive(int start, int end){ if(start<=end){ int temp = a[start]; a[start] = a[end]; a[end] = temp; start++; end—; reverseRecursive(start, end); } } public static void main(String[] args) { a = new int []{1,2,3,4,5}; System.out.println("Original Array" + Arrays.toString(a)); reverseIteration(); System.out.println("Reversed – Array(Iteration):" + Arrays.toString(a)); reverseRecursive(0,a.length–1); System.out.println("Reversed Again – Array(Recursion):" + Arrays.toString(a)); } }

Output:

```Original Array[1, 2, 3, 4, 5]
Reversed - Array(Iteration):[5, 4, 3, 2, 1]
Reversed Again - Array(Recursion):[1, 2, 3, 4, 5]
```

### 2 thoughts on “Reverse the given Array without using built in function”

1. Thanks for sharing this program. Here is an alternate C program to reverse an array using recursion.

2. package datastructues;

public class ReverseArray {

static int[] a = new int[] { 1, 2, 3, 4, 11, 10, 5, 6, 7, 8 };

public static void main(String[] args) {

for(int k = a.length-1; k>=0; k–)
{
System.out.println(a[k]);
}

recurse(a, a.length -1);

int[] reverseArray = reverseArray(a);

System.out.println(reverseArray);
}
private static void recurse(int[] a, int total) {
if(total >= 0)
{
System.out.println(a[total]);
recurse(a, –total);
}
}

private static int[] reverseArray(int[] a)
{
for (int i = 1; i <= a.length / 2; i++) {
a[i-1] = a[i-1] + a[a.length-i];
a[a.length-i] = a[i-1] – a[a.length-i];
a[i-1] = a[i-1] – a[a.length-i];
}
return a;
}
}