CODEWITHSUNDEEP
javaarraysrecursionboolean
Michelle Roxanne Lopez
Michelle Roxanne Lopez

Reputation: 31

how do you write out if an element is a member of an array in a boolean statement that is also recursive?

I don't know what to put for the if statement, I am working on this for class and am still EXTREMELY new to the language. It needs to recursively return true if element x is a member of an array A[] and false if not.

public static Boolean member (int x, int A[])
{
   if (     )//base case
       return true;
   else // general case
{

      int[] T= new int [A.length-1];
      for (int i=1; I<A.length; i++)
            T[i-1]=A[i];
      return false;
  }
}

Upvotes: 1

Views: 317

Answers (3)

alainlompo
alainlompo

Reputation: 4434

Here is another way of doing it: I tried to respect your initial code flow

public static Boolean member (int x, int A[])
{
   if ( x == A[0]    )//base case
       return true;
   else // general case
{

     if (A.length == 1) {
         return false;
     }
     int B[] = new int[A.length-1];
     System.arraycopy(A, 1, B, 0, B.length);
     return member(x, B);
  }
}

A test example

public static void main(String[] args) {
    
    int A[] = {5,6,7,8,11,25,135,256,1875,1254};
    boolean membershipOf25 = member(25,A);
    System.out.println("Is 25 member? " + membershipOf25);
    
    boolean membershipOf256 = member(256,A);
    System.out.println("Is 256 member? " + membershipOf256);
    
    boolean membershipOf109 = member(109,A);
    System.out.println("Is 109 member? " + membershipOf109);
    
    
}

The result:

Is 25 member? true

Is 256 member? true

Is 109 member? false

Upvotes: 0

kockburn
kockburn

Reputation: 17616

Made a project and this works. 

package recursiveTest;

public class test {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int [] test = new int[10];
        for(int i = 0; i < 10; i++){
            test[i] = i;
        }
        System.out.println(member(4, test));
    }
    public static Boolean member (int x, int A[])
    {
        Boolean res = false;
        if(A.length > 0){
            if(A[0] != x){
                int [] A_NEW = CreateANew(A);
                res = member(x, A_NEW);
            }else{
                res = true;
            }
        }
        return res;

    }
    public static int[] CreateANew(int A[]){
        int [] A_NEW = new int [A.length-1];
        for(int i = 1; i < A.length; i++){
            A_NEW[i-1] = A[i];
        }
        return A_NEW;
    }
}

Upvotes: 0

peter.petrov
peter.petrov

Reputation: 39457

Say you have this function/method: search(array a, int x, int index)
(1) check if index == a.length, if yes - return false;
(2) check if x is equal to the element a[index], if yes - return true;
(3) otherwise call and return search(a, x, index + 1)

This the pseude-code, you just need to write it in Java.
The function search is recursive.

Upvotes: 1

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