Longest common suffix of two linked lists

Given two singly linked lists, find the Longest common suffix of two linked lists. If there are no common characters which are suffixes, return the minimum length of the two linked lists.

Examples:

Input : list1 = w -> a -> l -> k -> i -> n -> g
        list2 = l -> i -> s -> t -> e -> n -> i -> n -> g
Output :i -> n -> g

Input : list1 = p -> a -> r -> t -> y
        list2 = p -> a -> r -> t -> y -> i -> n -> g
Output :p -> a -> r -> t -> y

A simple solution is to use auxiliary arrays to store linked lists. Then print longest commons suffix of two arrays.
The above solution requires extra space. We can save space by first doing reverse of both linked lists. After reversing, we can easily find length of longest common prefix. Reversing again to get the original lists back. 

One important point here is, order of elements. We need to print nodes from n-th to end. We use the above found count and print nodes in required order using two pointer approach. 

Implementation:

C++

// C++ program to find the Longest Common
// suffix in linked lists
#include <bits/stdc++.h>
using namespace std;

/* Linked list node */
struct Node
{
    char data;
    struct Node* next;
};

/* Function to insert a node at the beginning of
   the linked list */
void push(struct Node **head_ref, int new_data)
{
    struct Node* new_node = new Node;
    new_node->data = new_data;
    new_node->next = *head_ref;
    *head_ref = new_node;
}

/* Function to reverse the linked list */
struct Node *reverseList(struct Node *head_ref)
{
    struct Node *current, *prev, *next;
    current = head_ref;
    prev = NULL;

    while (current != NULL)
    {
        next = current->next;
        current->next = prev;
        prev = current;
        current = next;
    }
    return prev;
}


// Utility function to print last n nodes
void printLastNNode(struct Node* head, int n)
{
    // if n == 0
    if (n <= 0)
        return;

    // Move reference pointer n positions ahead
    struct Node* ref_ptr = head;
    while (ref_ptr != NULL && n--)
        ref_ptr = ref_ptr->next;

    // Now move main and reference pointers at
    // same speed. By the end of this loop,
    // reference pointer would point to end and
    // main pointer would point to n-th node
    // from end.
    Node *main_ptr = head;
    while (ref_ptr != NULL) {
        main_ptr = main_ptr->next;
        ref_ptr = ref_ptr->next;
    }

    // Print last n nodes.
    while (main_ptr != NULL)
    {
       cout << main_ptr->data;
       main_ptr = main_ptr->next;
    }
}

// Prints the Longest Common suffix in
// linked lists
void longestCommSuffix(Node *h1, Node *h2)
{
    // Reverse Both Linked list
    h1 = reverseList(h1);
    h2 = reverseList(h2);

    // Now we print common nodes from head
    Node *temp1 = h1, *temp2 = h2;
    int count = 0;
    while (temp1!=NULL&&temp2!=NULL)
    {
        // If a node is not common, break
        if (temp1 -> data != temp2 -> data)
            break;

        // Keep printing while there are
        // common nodes.
        count++;
        temp1 = temp1 -> next;
        temp2 = temp2 -> next;
    }

    // Reversing linked lists to retain
    // original lists.
    h1 = reverseList(h1);
    h2 = reverseList(h2);

    printLastNNode(h1, count);
}

// Driver program to test above
int main()
{
    struct Node *h1 = NULL, *h2 = NULL;

    // creating the 1 linked list
    push(&h1,'g');
    push(&h1,'n');
    push(&h1,'i');
    push(&h1,'k');
    push(&h1,'l');
    push(&h1,'a');
    push(&h1,'w');

    // creating the 2 linked list
    push(&h2,'g');
    push(&h2,'n');
    push(&h2,'i');
    push(&h2,'n');
    push(&h2,'e');
    push(&h2,'t');
    push(&h2,'s');
    push(&h2,'i');
    push(&h2,'l');

    longestCommSuffix(h1, h2);

    return 0;
}

Java

// Java program to find the Longest Common
// suffix in linked lists
import java.util.*;
class GFG
{

/* Linked list node */
static class Node
{
    int data;
    Node next;
};
static Node h1,h2;

/* Function to insert a node at the beginning
of the linked list */
static Node push(Node head_ref, int new_data)
{
    Node new_node = new Node();
    new_node.data = new_data;
    new_node.next = head_ref;
    head_ref = new_node;
    return head_ref;
}

/* Function to reverse the linked list */
static Node reverseList(Node head_ref)
{
    Node current, prev, next;
    current = head_ref;
    prev = null;

    while (current != null)
    {
        next = current.next;
        current.next = prev;
        prev = current;
        current = next;
    }
    return prev;
}

// Utility function to print last n nodes
static void printLastNNode(Node head, int n)
{
    // if n == 0
    if (n <= 0)
        return;

    // Move reference pointer n positions ahead
    Node ref_ptr = head;
    while (ref_ptr != null && n-- > 0)
        ref_ptr = ref_ptr.next;

    // Now move main and reference pointers at
    // same speed. By the end of this loop,
    // reference pointer would point to end and
    // main pointer would point to n-th node
    // from end.
    Node main_ptr = head;
    while (ref_ptr != null)
    {
        main_ptr = main_ptr.next;
        ref_ptr = ref_ptr.next;
    }

    // Print last n nodes.
    while (main_ptr != null)
    {
        System.out.print((char)(main_ptr.data));
        main_ptr = main_ptr.next;
    }
}

// Prints the Longest Common suffix in
// linked lists
static void longestCommSuffix()
{
    // Reverse Both Linked list
    h1 = reverseList(h1);
    h2 = reverseList(h2);

    // Now we print common nodes from head
    Node temp1 = h1, temp2 = h2;
    int count = 0;
    while (temp1 != null && temp2 != null)
    {
        // If a node is not common, break
        if (temp1 . data != temp2 . data)
            break;

        // Keep printing while there are
        // common nodes.
        count++;
        temp1 = temp1 . next;
        temp2 = temp2 . next;
    }

    // Reversing linked lists to retain
    // original lists.
    h1 = reverseList(h1);
    h2 = reverseList(h2);

    printLastNNode(h1, count);
}

// Driver Code
public static void main(String[] args)
{
    h1 = null; h2 = null;

    // creating the 1 linked list
    h1 = push(h1, 'g');
    h1 = push(h1, 'n');
    h1 = push(h1, 'i');
    h1 = push(h1, 'k');
    h1 = push(h1, 'l');
    h1 = push(h1, 'a');
    h1 = push(h1, 'w');

    // creating the 2 linked list
    h2 = push(h2, 'g');
    h2 = push(h2, 'n');
    h2 = push(h2, 'i');
    h2 = push(h2, 'n');
    h2 = push(h2, 'e');
    h2 = push(h2, 't');
    h2 = push(h2, 's');
    h2 = push(h2, 'i');
    h2 = push(h2, 'l');

    longestCommSuffix();
}
}

// This code is contributed by Rajput-Ji

Python3

# Python3 program to find the Longest Common
# suffix in linked lists

# Link list node
class Node:

    def __init__(self, data):

        self.data = data
        self.next = None

# Function to insert a node at the
# beginning of the linked list
def push( head_ref, new_data):

    new_node = Node(new_data)
    new_node.next = head_ref
    head_ref = new_node

    return head_ref

# Function to reverse the linked list
def reverseList(head_ref):

    next = None
    current = head_ref
    prev = None

    while (current != None):
        next = current.next
        current.next = prev
        prev = current
        current = next

    return prev

# Utility function to print last n nodes
def printLastNNode(head, n):

    # If n == 0
    if (n <= 0):
        return

    # Move reference pointer n positions ahead
    ref_ptr = head

    while (ref_ptr != None  and n != 0):
        n -= 1
        ref_ptr = ref_ptr.next

    # Now move main and reference pointers at
    # same speed. By the end of this loop,
    # reference pointer would point to end and
    # main pointer would point to n-th node
    # from end.
    main_ptr = head

    while (ref_ptr != None):
        main_ptr = main_ptr.next
        ref_ptr = ref_ptr.next

    # Print last n nodes.
    while (main_ptr != None):
        print(main_ptr.data, end = '')

        main_ptr = main_ptr.next

# Prints the Longest Common suffix in
# linked lists
def longestCommSuffix(h1, h2):

    # Reverse Both Linked list
    h1 = reverseList(h1)
    h2 = reverseList(h2)

    # Now we print common nodes from head
    temp1 = h1
    temp2 = h2
    count = 0

    while (temp1 != None and temp2 != None):

        # If a node is not common, break
        if (temp1.data != temp2.data):
            break

        # Keep printing while there are
        # common nodes.
        count += 1
        temp1 = temp1.next
        temp2 = temp2.next

    # Reversing linked lists to retain
    # original lists.
    h1 = reverseList(h1)
    h2 = reverseList(h2)

    printLastNNode(h1, count)

# Driver code
if __name__=='__main__':

    h1 = None
    h2 = None

    # Creating the 1 linked list
    h1 = push(h1, 'g')
    h1 = push(h1, 'n')
    h1 = push(h1, 'i')
    h1 = push(h1, 'k')
    h1 = push(h1, 'l')
    h1 = push(h1, 'a')
    h1 = push(h1, 'w')

    # Creating the 2 linked list
    h2 = push(h2, 'g')
    h2 = push(h2, 'n')
    h2 = push(h2, 'i')
    h2 = push(h2, 'n')
    h2 = push(h2, 'e')
    h2 = push(h2, 't')
    h2 = push(h2, 's')
    h2 = push(h2, 'i')
    h2 = push(h2, 'l')

    longestCommSuffix(h1, h2)

# This code is contributed by rutvik_56

C#

// C# program to find the Longest Common
// suffix in linked lists
using System;

class GFG
{

/* Linked list node */
public class Node
{
    public int data;
    public Node next;
};
static Node h1, h2;

/* Function to insert a node
at the beginning of the linked list */
static Node push(Node head_ref,
                 int new_data)
{
    Node new_node = new Node();
    new_node.data = new_data;
    new_node.next = head_ref;
    head_ref = new_node;
    return head_ref;
}

/* Function to reverse the linked list */
static Node reverseList(Node head_ref)
{
    Node current, prev, next;
    current = head_ref;
    prev = null;

    while (current != null)
    {
        next = current.next;
        current.next = prev;
        prev = current;
        current = next;
    }
    return prev;
}

// Utility function to print last n nodes
static void printLastNNode(Node head, int n)
{
    // if n == 0
    if (n <= 0)
        return;

    // Move reference pointer n positions ahead
    Node ref_ptr = head;
    while (ref_ptr != null && n-- > 0)
        ref_ptr = ref_ptr.next;

    // Now move main and reference pointers at
    // same speed. By the end of this loop,
    // reference pointer would point to end and
    // main pointer would point to n-th node
    // from end.
    Node main_ptr = head;
    while (ref_ptr != null)
    {
        main_ptr = main_ptr.next;
        ref_ptr = ref_ptr.next;
    }

    // Print last n nodes.
    while (main_ptr != null)
    {
        Console.Write((char)(main_ptr.data));
        main_ptr = main_ptr.next;
    }
}

// Prints the Longest Common suffix in
// linked lists
static void longestCommSuffix()
{
    // Reverse Both Linked list
    h1 = reverseList(h1);
    h2 = reverseList(h2);

    // Now we print common nodes from head
    Node temp1 = h1, temp2 = h2;
    int count = 0;
    while (temp1 != null && temp2 != null)
    {
        // If a node is not common, break
        if (temp1 . data != temp2 . data)
            break;

        // Keep printing while there are
        // common nodes.
        count++;
        temp1 = temp1 . next;
        temp2 = temp2 . next;
    }

    // Reversing linked lists to retain
    // original lists.
    h1 = reverseList(h1);
    h2 = reverseList(h2);

    printLastNNode(h1, count);
}

// Driver Code
public static void Main(String[] args)
{
    h1 = null; h2 = null;

    // creating the 1 linked list
    h1 = push(h1, 'g');
    h1 = push(h1, 'n');
    h1 = push(h1, 'i');
    h1 = push(h1, 'k');
    h1 = push(h1, 'l');
    h1 = push(h1, 'a');
    h1 = push(h1, 'w');

    // creating the 2 linked list
    h2 = push(h2, 'g');
    h2 = push(h2, 'n');
    h2 = push(h2, 'i');
    h2 = push(h2, 'n');
    h2 = push(h2, 'e');
    h2 = push(h2, 't');
    h2 = push(h2, 's');
    h2 = push(h2, 'i');
    h2 = push(h2, 'l');

    longestCommSuffix();
}
}

// This code is contributed by PrinciRaj1992

Javascript

<script>

// JavaScript program to find the Longest Common
// suffix in linked lists

/* Linked list node */
class Node
{
    constructor()
    {
        this.data = 0;
        this.next = null;
    }
};

var h1, h2;

/* Function to insert a node
at the beginning of the linked list */
function push(head_ref, new_data)
{
    var new_node = new Node();
    new_node.data = new_data;
    new_node.next = head_ref;
    head_ref = new_node;
    return head_ref;
}

/* Function to reverse the linked list */
function reverseList(head_ref)
{
    var current, prev, next;
    current = head_ref;
    prev = null;

    while (current != null)
    {
        next = current.next;
        current.next = prev;
        prev = current;
        current = next;
    }
    return prev;
}

// Utility function to print last n nodes
function printLastNNode(head, n)
{
    // if n == 0
    if (n <= 0)
        return;

    // Move reference pointer n positions ahead
    var ref_ptr = head;
    while (ref_ptr != null && n-- > 0)
        ref_ptr = ref_ptr.next;

    // Now move main and reference pointers at
    // same speed. By the end of this loop,
    // reference pointer would point to end and
    // main pointer would point to n-th node
    // from end.
    var main_ptr = head;
    while (ref_ptr != null)
    {
        main_ptr = main_ptr.next;
        ref_ptr = ref_ptr.next;
    }

    // Print last n nodes.
    while (main_ptr != null)
    {
        document.write((main_ptr.data));
        main_ptr = main_ptr.next;
    }
}

// Prints the Longest Common suffix in
// linked lists
function longestCommSuffix()
{
    // Reverse Both Linked list
    h1 = reverseList(h1);
    h2 = reverseList(h2);

    // Now we print common nodes from head
    var temp1 = h1, temp2 = h2;
    var count = 0;
    while (temp1 != null && temp2 != null)
    {
        // If a node is not common, break
        if (temp1 . data != temp2 . data)
            break;

        // Keep printing while there are
        // common nodes.
        count++;
        temp1 = temp1 . next;
        temp2 = temp2 . next;
    }

    // Reversing linked lists to retain
    // original lists.
    h1 = reverseList(h1);
    h2 = reverseList(h2);

    printLastNNode(h1, count);
}

// Driver Code
h1 = null; h2 = null;
// creating the 1 linked list
h1 = push(h1, 'g');
h1 = push(h1, 'n');
h1 = push(h1, 'i');
h1 = push(h1, 'k');
h1 = push(h1, 'l');
h1 = push(h1, 'a');
h1 = push(h1, 'w');
// creating the 2 linked list
h2 = push(h2, 'g');
h2 = push(h2, 'n');
h2 = push(h2, 'i');
h2 = push(h2, 'n');
h2 = push(h2, 'e');
h2 = push(h2, 't');
h2 = push(h2, 's');
h2 = push(h2, 'i');
h2 = push(h2, 'l');
longestCommSuffix();

</script>

Output

ing

Time Complexity : O(N)

Auxiliary Space: O(1)