Java Help: Please answer both parts of the question fully:

(a). Given two linked lists of Strings that are each sorted in alphabetical order from head to tail, produce a third linked list which contains the strings from both linked lists and also sorted from head to tail. Note that there could be some duplicate strings in either or both lists. You can use compareTo(..) method of String class for comparing two strings for alphabetical ordering.

(b). Given an array of integers, and given a specific value k (not equal to 0), produce all unique pairs of values in the array which differ by k. For example, if the array has [1,4,9,12, 6, 15, 5, 13,17] and k=3, the answer would be (1,4 ) ( 9,12), ( 9,6), (12,15). If k=4, the answer would be (1,5), (9,5), (13,17), (13,9)