reverse and print an array using recursive method

Question

the method below works fine, but I can't find a way to print the reversed array using same method. I tried for-each loop but it print three arrays not just one. for example if the inputs:

size 5, start=1, end=5, arr[] ={1,2,3,4,5}

output:

543215432154321

correct output should be

54321

here is the code:

static void reverse(int[] arr, int start, int end) {
    if (start < end) {
        int temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
        reverse(arr, start + 1, end - 1);       
    }   

    for (int pr : arr) {
        System.out.print(pr);
    }
}

Shouldn't your initial call be start = 0 and end = 4 since arrays index starting at zero? And your function prints the entire array on every call, so you are getting it output multiple times. — lurker
– lurker, Commented Oct 19, 2015 at 16:41
return the array as result and then in the calling method print the content in for loop — Neenad
– Neenad, Commented Oct 19, 2015 at 16:43
If it's all working for you now, you should accept an answer. — NickJ
– NickJ, Commented Oct 19, 2015 at 17:01

NickJ · Accepted Answer · 2015-10-19 16:43:20Z

7

You are very very close.

The only mistake you are making is printing the result from inside the reverse method - don't forget it's recursive so you'll get intermediate results printed.

Instead, call in first from another method, then print it out:

public static void main(String[] args) {
    int[] arr = {1,2,3,4,5,6,7,8,9,0};
    reverse(arr,0,arr.length-1);
    for (int pr : arr) {
        System.out.print(pr);
    }
}

static void reverse(int[] arr, int start, int end) {
    if (start < end) {
        int temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
        reverse(arr, start + 1, end - 1);
    }
}

answered Oct 19, 2015 at 16:43

NickJ

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1 Comment

lurker Over a year ago

The second mistake of the OP's which you corrected but didn't mention is indexing the array originally from 0 to length-1 instead of 1 to length. :)

phositronax · Accepted Answer · 2015-10-19 16:56:42Z

1

You are printing out the array everytime it calls 'reverse' method . I have modified a bit of your code. And its working fine.

static void reverse(int[] arr, int start, int end) {
    if (start < end) {
        int temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;
    reverse(arr, start + 1, end - 1);       
    } 
    else {
     for (int pr : arr) {
        System.out.print(pr);
    }

Since size of your array is 5, you should be doing something like this

reverse (myArray,0,4);

answered Oct 19, 2015 at 16:56

phositronax

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Comments

SSG989 · Accepted Answer · 2017-10-28 01:38:42Z

0

public static void main(String[] args) {

 //assume u have create an array;
    System.out.print("this array reversely equal to : ");
    ArrayReverse(array, 0);
}

public static void ArrayReverse(int[] a, int index) {

    if (index > a.length - 1) {
        return;
    }
    ArrayReverse(a, index + 1);
    System.out.print(a[index] + " ");

}

answered Oct 28, 2017 at 1:38

SSG989

1

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