How to find the occurence of an array in another array? and returning indexes of the first array

Question

This is the algorithm I am trying to complete but don't know how to move forward ,

public int findArray(int[] array, int[] subArray) {
    for (int i = 0; i < array.length; i++) {
        for (int j = 0; i < subArray.length; j++) {
            if (array[i] == subarray[j]) {//not sure if this is how to start 

            }
        }//will want to compare all element in subarray to Array
    }
    return 0;
}

My desired result would be as follows

//[4,9,3,7,8] and [3,7] should return 2.
//[7,8,9] and [8,9,10] should return -1

//[4,9,3,7,8,3,7,1] and [3,7]should return 5

My understanding is I take subarray as whole and try to find where it matches in the array but don't know how to go about it

Answer 1

One simple approach:

// 1) Convert array to String, for eg. [1,2,3,4] => "1234". 
// 2) Use Strings substring/lastIndexOf to find the correct index. 

private static int findSubarrayPosition(int[] array, int[] subarray) {
      StringBuilder sb = new StringBuilder();
      for (int i = 0; i < array.length; i++) {
          sb.append(array[i]);
      }
      String string = sb.toString();

      sb = new StringBuilder();
      for (int i = 0; i < subarray.length; i++) {
          sb.append(subarray[i]);
      }
      String subString = sb.toString();

      return string.lastIndexOf(subString);
}

Answer 2

Try following code. You have to check for first element in the sub array and then other elements.

public static int findArray(int[] array, int[] subArray) {
    int index = -1;
    arrayLoop : for (int i= 0; i<array.length; i++){
        if(array[i] == subArray[0]){
            for (int j=1; j<subArray.length; j++){
                if (i+j>array.length-1 || array[i+j]!=subArray[j]) continue arrayLoop;
            }
            index = i;
        }
    }
    return index;
}

Check your test cases with following code.

public static void main(String[] args) {
    int[] array1 = {4,9,3,7,8};  int[] subArray1 = {3,7};
    System.out.println(findArray(array1, subArray1));

    int[] array2 = {7,8,9};  int[] subArray2 = {8,9,10};
    System.out.println(findArray(array2, subArray2));

    int[] array3 = {4,9,3,7,8,3,7,1};  int[] subArray3 = {3,7};
    System.out.println(findArray(array3, subArray3));

}