How to get an output based on 2 different arrays

Question

I'm having trouble creating an output based on 2 different arrays. For example, I have 2 arrays "A" and "B". I sorted the elements in ascending order using this method:

public static void sortOrder(int [] A) {
    for(int i = 0; i < A.length; i++) {
        for(int k = i + 1; k < A.length; k++) {
            if(A[i] > A[k]) {
                int temp = A[i];
                A[i] = A[k];
                A[k] = temp;
            }
        } 
    }
}

I want to output the B[i]th smallest number in array A.

For example, after sorting, array A = [3, 5, 7, 8, 11, 21] and B is [1, 3, 5].

The desired output is [3, 7, 11] as the 1st smallest element of A is 3, the 3rd smallest element of A is 7, and the 5th smallest element of A is 11.

So far this is what I came up with:

public static void Algorithm1(int [] A, int [] B) {
    sortOrder(A);
    sortOrder(B);
    
    int[] result = new int[B.length];
    int min = A[0];
    
    for(int i = 0; i < A.length; i++) {
        for(int k = 0; k < B.length; k++) {
            if(B[k] <= min) {
                result[k] = A[k];
            }
        }
    }
    System.out.println(Arrays.toString(result));
    //A is [3, 5, 7, 8, 11, 21]
    //B is [1, 3, 5]
    //Desired output is [3, 7, 11]
    }

Running this code I get an output of [3, 5, 0]. I know the problem probably lies with the nested for loop but for the life of me I cannot figure out how to solve it. Sorry if I didn't explain what I want clearly enough as I am still quite new to programming.

Thanks in advance!!

Answer 1

You do not need to have a nested loop and go through both arrays, you simply need to loop through the result.length or B.length (as they are always equal) and take the value of B[i] - 1 and use it as the index to access A. This leaves you with result[i] = A[B[i] - 1];.

Fixed Code:

public static void Algorithm1(int [] A, int [] B) {
    sortOrder(A);
    sortOrder(B);
    
    int[] result = new int[B.length];
    
    for(int i = 0; i < result.length; i++) {
        result[i] = A[B[i] - 1];
    }
    System.out.println(Arrays.toString(result));
}

Test Run:

public static void main(String args[]) throws Exception {
    
    int [] arr1 = new int[]{21, 8, 11, 7, 5, 3};
    int [] arr2 = new int[]{3, 5, 1};

    Algorithm1(arr1, arr2);
    
}

Output:

[3, 7, 11]