Determine the symmetric difference of multiple lists of numbers

DoubleList.java

/*
  Given a multiple sorted lists, determine the unique elements (symmetric difference).
  https://en.wikipedia.org/wiki/Symmetric_difference
*/

import java.util.*;

class DoubleList
{
  public static void main (String [] args)
  {
    Scanner sc = new Scanner(System.in);

    int[] a = new int[sc.nextInt()];

    for(int i = 0; i < a.length; i++) {
      a[i] = sc.nextInt();
    }

    int[] b = new int[sc.nextInt()];

    for(int i = 0; i < b.length; i++) {
      b[i] = sc.nextInt();
    }

    ArrayList<Integer> ans = symmetricDiff(a, b);
    
    for(int i = 0; i < ans.size(); i++) {
      System.out.print(ans.get(i) + " ");
    }
  }

  // Two list case
  public static ArrayList<Integer> symmetricDiff(int[] a, int[] b) {
    int i = 0;
    int j = 0;

    ArrayList<Integer> ans = new ArrayList<Integer>();

    while(i < a.length && j < b.length) {
      if(a[i] == b[j]) {
        i++;
        j++;
      } else if(a[i] < b[j]) {
        ans.add(a[i]);
        i++;
      } else {
        ans.add(b[j]);
        j++;
      }
    }

    for(; i < a.length; i++) {
      ans.add(a[i]);
    }

    for(; j < b.length; j++) {
      ans.add(b[j]);
    }

    return ans;
  }

  // Multiple list case
  public static int symmetricDiff(ArrayList<int[]> llist) {
    // List of counters
    int[] i = new int[llist.length];

    for(int j = 0; j < llist.length(); j++) {
      i[j] = 0;
    }

    // TODO Solution
  }
}