Exception in thread "main" java.lang.NumberFormatException: For input string: ""
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:592)
at java.lang.Integer.parseInt(Integer.java:615)
at TestClass.main(TestClass.java:66)

idvInput = Integer.parseInt(idvInputString);

import java.io.BufferedReader;
import java.io.InputStreamReader;

//import for Scanner and other utility classes
import java.util.*;


// Warning: Printing unwanted or ill-formatted data to output will cause the test cases to fail

class TestClass {
    public static void main(String args[] ) throws Exception {
        /* Sample code to perform I/O:
         * Use either of these methods for input

        //BufferedReader
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String name = br.readLine();                // Reading input from STDIN
        System.out.println("Hi, " + name + ".");    // Writing output to STDOUT

        //Scanner
        Scanner s = new Scanner(System.in);
        String name = s.nextLine();                 // Reading input from STDIN
        System.out.println("Hi, " + name + ".");    // Writing output to STDOUT

        */

        // Write your code here
        LinkedList<Integer>[] inputArray;

        Scanner s = new Scanner(System.in);
        System.out.println("Enter the number of test cases you wish to run");
        String numCasesString = s.nextLine();
        int numCases = Integer.parseInt(numCasesString);

        for (int i = 0; i < numCases; i++){
            System.out.println("Enter the number of elements (n) in array A");
            String numElementsString = s.nextLine();
            int numElements = Integer.parseInt(numElementsString);

            inputArray = new LinkedList[numElements];
            for (int k = 0; k < inputArray.length; k++){
                inputArray[k] = new LinkedList<Integer>();
            }

            System.out.println("Enter the elements in aray A");
            String inputString = s.nextLine();

            String idvInputString;
            int idvInput;
            int j = 0;
            int k = 0;
            while (true){
                j = inputString.indexOf(" ", j + 1);
                if (j < 0){
                    //System.out.println("last number; j = " + j + "; k = " + k);
                    idvInputString = inputString.substring(k, inputString.length());
                }
                else{
                    //System.out.println("j = " + j + "; k = " + k);
                    idvInputString = inputString.substring(k, j);
                }
                System.out.println(idvInputString);
                idvInput = Integer.parseInt(idvInputString);
                write(inputArray, idvInput);
                k = j + 1;
                if (j < 0) { break;}
            }

            System.out.println("Enter the number of queries");
            String numQueriesString = s.nextLine();
            int numQueries = Integer.parseInt(numQueriesString);
            String queryString;
            int query;
            for (int z = 0; z < numQueries; z++){
                System.out.println("Enter the number to query");
                queryString = s.nextLine();
                query = Integer.parseInt(queryString);
                lookup(inputArray, query);
            }


        }

    }

    public static int hash(int x, int numElem){
        return Math.abs(x) % numElem;
    }

    public static void lookup(LinkedList<Integer>[] array, int x) {
        int hashCode = hash(x, array.length);
        for (int item : array[hashCode]) {
            if (item == x) {
                System.out.println("Yes");
                return;
            }
        }
        System.out.println("No");
        return;
    }

    public static void write(LinkedList<Integer>[] array, int x) {
        int hashcode = hash(x, array.length);
        array[hashcode].push(x);
    }
}

while (true){
                j = inputString.indexOf(" ", j + 1);
                if (j < 0){
                    //System.out.println("last number; j = " + j + "; k = " + k);
                    idvInputString = inputString.substring(k, inputString.length());
                }
                else{
                    //System.out.println("j = " + j + "; k = " + k);
                    idvInputString = inputString.substring(k, j);
                }
                System.out.println(idvInputString);
                idvInput = Integer.parseInt(idvInputString);
                write(inputArray, idvInput);
                k = j + 1;
                if (j < 0) { break;}
            }