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Basically I have university work about recursion but I'm having problems solving this. I have to create two methods, one called getLastElement and isSymmetric. getLastElement can only access index 0 from the array. isSymmetric must print true if the array is symmetric or if it's 0. It must use array[0] and array.length. It can also use Arrays.copyOfRange()

I already made isSymmetric but without getLastElement and I think I'm missing something since I don't know how to incorporate getLastElement into it. I know I didn't use array[0] but I couldn't get the code working with it.

Here's my code:

public static int isSymmetric(int array[], int begin, int end) 
    { 

        if (begin >= end) { 
            return 1; 
        } 
        if (array[begin] == array[end]) { 
            return isSymmetric(array, begin + 1, end - 1); 
        } 
        else { 
            return 0; 
        } 
    } 


        public static void main (String[] args) { 
        int array[] = { 1, 2, 3, 2, 1 }; 

        if (isSymmetric(array, 0, array.length - 1) == 1) 
            System.out.print( "true"); 
        else
            System.out.println( "false"); 
        }

I just want to print just like I am right now but with getLastElement incorporated into isSymmetric.

  • can you explain more about your `getLastElement` function? – prashantpiyush Apr 15 '19 at 14:32
  • It says that it's restricted to only access the index 0 element. It's the only thing it says on the pdf my teacher gave me. Sorry if you can't understand it, I translated it from my language and it may have lost some meaning. –  Apr 15 '19 at 14:35
  • possible duplicate of https://stackoverflow.com/questions/15299312/checking-if-array-is-symmetric ? – Michał Krzywański Apr 15 '19 at 14:37
  • I think the person asking you this expect you to create a new array in the function `isSymmetric()` that contain all element af the input array except the firs and last element. While what you are doing is passing the whole array, and tell the function where to start and where to end. – vincrichaud Apr 15 '19 at 14:42

1 Answers1

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Instead of sending the whole array along with the indices begin and end, you can just use a copy of the array between these two indices. Doing this will allow you to use your getLastElement function (see code).

// I am assuming this function returns the 
// 0th-indexed element of the array.
public static int getLastElement(int[] array) {
    return array[0];    
}

public static int isSymmetric(int[] array) {
    if(array.length <= 1) return 1;

    // check if the first and the last element are equal
    if(getLastElement(array) == array[array.length -1])

        // copy the remaining array (leaving first and last element)
        return isSymmetric(Arrays.copyOfRange(array, 1, array.length-1));

    return 0;
}


public static void main (String[] args) { 
    int array[] = { 1, 2, 3, 2, 1 }; 

    if (isSymmetric(array) == 1) 
        System.out.println( "true"); 
    else
        System.out.println( "false"); 
}

getLastElement is actually returning the first element of the array, so if you see it is actually a getFristElement kind of function. This was done because the question states that this function is only allowed to access the 0th-index of the array.

prashantpiyush
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