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