Linked list for java:

I have already started it but now I am stuck; can anyone help me out? I want to iterate over the linked list and if the string has any characters I want to add it to an int value. If it has any of the same characters then just skip over it. Please ask if you have any questions

* * numUnique returns the number of unique values the list * Precondition: the list is not empty and is sorted from low to high. { your solution can assume this is true } * * * For full credit, your solution must go through the list exactly once. * Your solution may not call any other functions. * * * == * Examples: ["abcdef"] . numUnique () ["aaabcd"). numUnique () ["bccddee"]. numUnique () ["abcddd"].numUnique () ["a"].numUnique (). * == == * * * public int numUnique(int num, String r) { int sum = 0; for(Node newNode = first; newNode.next != null; newNode = newNode. next) { while(newNode.next.equals (num)) { sum++; return sum