Python Program For Comparing Two Strings Represented As Linked Lists

Given two strings, represented as linked lists (every character is a node in a linked list). Write a function compare() that works similar to strcmp(), i.e., it returns 0 if both strings are the same, 1 if the first linked list is lexicographically greater, and -1 if the second string is lexicographically greater.
Examples:

Input: list1 = g->e->e->k->s->a
       list2 = g->e->e->k->s->b
Output: -1

Input: list1 = g->e->e->k->s->a
       list2 = g->e->e->k->s
Output: 1

Input: list1 = g->e->e->k->s
       list2 = g->e->e->k->s
Output: 0

Python

# Python program to compare two strings
# represented as linked lists

# A linked list node
# structure
class Node:

    # Constructor to create
    # a new node
    def __init__(self, key):
        self.c = key ;
        self.next = None

def compare(list1, list2):

    # Traverse both lists. Stop when
    # either end of linked list is
    # reached or current characters
    # don't match
    while(list1 and list2 and
          list1.c == list2.c):
        list1 = list1.next
        list2 = list2.next

    # If both lists are not empty,
    # compare mismatching characters
    if(list1 and list2):
        return 1 if list1.c > list2.c else -1

    # If either of the two lists has
    # reached end
    if (list1 and not list2):
        return 1

    if (list2 and not list1):
        return -1
    return 0

# Driver code
list1 = Node('g')
list1.next = Node('e')
list1.next.next = Node('e')
list1.next.next.next = Node('k')
list1.next.next.next.next = Node('s')
list1.next.next.next.next.next = Node('b')

list2 = Node('g')
list2.next = Node('e')
list2.next.next = Node('e')
list2.next.next.next = Node('k')
list2.next.next.next.next = Node('s')
list2.next.next.next.next.next = Node('a')

print compare(list1, list2)
# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

Output:

1

Time Complexity: O(M + N), where M and N represents the length of the given two linked lists.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

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