CODEWITHSUNDEEP
java
1727977
1727977

Reputation: 47

Make a new array with common elements in two arrays

I have to create a method, that returns an array with common elements from two different arrays. I am aware there are lots of questions about this, but mine is a little bit different from those as I have to create a new array.

I've tried to first count how many common elements there are from two arrays, and then create an array with size the number of that.

After, I tried to set the new array to the common elements using a for loop.

public static int [] commonElements(int []a, int [] b){
      int count=0;
      for(int i=0;i<a.length;i++) {
         for(int j=0;j<b.length;j++) {
           if(a[i] == b[j]) {
             count++;
           }
        }
     }
     int []array= new int[count];

     for(int i=0;i<a.length;i++) {
        for(int j=0;j<b.length;j++) {
           if(a[i] == b[j]) {
              for (int k=0; k<count; k++){

                 array[k]=a[i];
             }
          }
       }
    }
    return array;
 }

This returns four -1's, so it doesn't work. I am also required not to use arraylist, so I have no idea how to make this code complete. The expected value with 

  // checking common elements
  System.out.println ("\nLooking for common elements in the arrays "); 
  int [] arr3= {56, -21, -5, 7, 10,  21, 2, -1};
  int [] arr4= {-1, -56, 5, 21, 3 , 7, 4, -6, 2, 90};
  int [] result4 = commonElements(arr3, arr4);
  System.out.println (Arrays.toString(arr3));
  System.out.println (Arrays.toString(arr4));  
  System.out.print ("\nCommon elements array:  ");
  System.out.println (Arrays.toString(result4));

in the main is 

     Looking for common elements in the arrays 
      [56, -21, -5, 7, 10, 21, 2, -1]
      [-1, -56, 5, 21, 3, 7, 4, -6, 2, 90]

      Common elements array:  [7, 21, 2, -1]

Any help would be greatly appreciated!

Upvotes: 1

Views: 2530

Answers (2)

Elliott Frisch
Elliott Frisch

Reputation: 201447

First, instead of int []array= new array[count]; you need new int[count]; - second, instead of a third inner loop when populating your output keep a position index and increment it when you encounter a duplicate. Like,

public static int[] commonElements(int[] a, int[] b) {
    int count = 0;
    for (int i = 0; i < a.length; i++) {
        for (int j = 0; j < b.length; j++) {
            if (a[i] == b[j]) {
                count++;
            }
        }
    }
    int[] array = new int[count];
    int p = 0;
    for (int i = 0; i < a.length; i++) {
        for (int j = 0; j < b.length; j++) {
            if (a[i] == b[j]) {
                array[p] = a[i];
                p++;
            }
        }
    }
    return array;
}

Alternatively, if using Java 8+, the above can be simplified by filtering on an IntStream of the two arrays. Like,

return Arrays.stream(a).filter(i -> Arrays.stream(b).anyMatch(x -> x == i))
        .toArray();

Upvotes: 0

Tim Biegeleisen
Tim Biegeleisen

Reputation: 521249

You might want to use a list to store the intermediate intersecting values, and then convert to an array at the end of the method:

public static int[] commonElements(int[] a, int[] b) {
    List<Integer> common = new ArrayList<>();

    for (int i=0; i < a.length; i++) {
        for(int j=0; j < b.length; j++) {
            if (a[i] == b[j]) {
                common.add(a[i]);
            }
        }
    }

    int[] array = common.stream().mapToInt(Integer::intValue).toArray();
    return array;
}

If you don't want to record duplicates, then replace common with Set<Integer>.

Upvotes: 1

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