Given a set of strings, find the longest common prefix.
Examples:
Input : {“geeksforgeeks”, “geeks”, “geek”, “geezer”} Output : "gee" Input : {"apple", "ape", "april"} Output : "ap"
Previous Approaches: Word by Word Matching, Character by Character Matching, Divide and Conquer, Binary Search, Using Trie Data Structure
Below is an algorithm to solve above problem using Linked List.
- Create a linked list using the characters of the first string as the data in the linked list.
- Then one by one using all the remaining strings, iterate over the linked list deleting all the nodes after the point where the string gets exhausted or linked list gets exhausted or the characters do not match.
- The remaining data in linked list is the required longest common prefix.
Below is the implementation in C++
C++
// C++ Program to find the longest common prefix // in an array of strings #include <bits/stdc++.h> using namespace std;
// Structure for a node in the linked list struct Node {
char data;
Node* next;
}; // Function to print the data in the linked list // Remaining nodes represent the longest common prefix void printLongestCommonPrefix(Node* head)
{ // If the linked list is empty there is
// no common prefix
if (head == NULL) {
cout << "There is no common prefix\n" ;
return ;
}
// Printing the longest common prefix
cout << "The longest common prefix is " ;
while (head != NULL) {
cout << head->data;
head = head->next;
}
} // Function that creates a linked list of characters // for the first word in the array of strings void Initialise(Node** head, string str)
{ // We calculate the length of the string
// as we will insert from the last to the
// first character
int l = str.length();
// Inserting all the nodes with the characters
// using insert at the beginning technique
for ( int i = l - 1; i >= 0; i--) {
Node* temp = new Node;
temp->data = str[i];
temp->next = *head;
*head = temp;
}
// Since we have passed the address of the
// head node it is not required to return
// anything
} // Function to delete all the nodes // from the unmatched node till the end of the // linked list void deleteNodes(Node* head)
{ // temp is used to facilitate the deletion of nodes
Node* current = head;
Node* next;
while (current != NULL) {
next = current->next;
free (current);
current = next;
}
} // Function that compares the character of the string with // the nodes of the linked list and deletes all nodes after // the characters that do not match void longestCommonPrefix(Node** head, string str)
{ int i = 0;
// Use the pointer to the previous node to
// delete the link between the unmatched node
// and its prev node
Node* temp = *head;
Node* prev = *head;
while (temp != NULL) {
// If the current string finishes or if the
// the characters in the linked list do not match
// with the character at the corresponding position
// delete all the nodes after that.
if (str[i] == '\0' || temp->data != str[i]) {
// If the first node does not match then there
// is no common prefix
if (temp == *head) {
free (temp);
*head = NULL;
}
// Delete all the nodes starting from the
// unmatched node
else {
prev->next = NULL;
deleteNodes(temp);
}
break ;
}
// If the character matches, move to next
// node and store the address of the current
// node in prev
prev = temp;
temp = temp->next;
i++;
}
} int main()
{ string arr[] = { "geeksforgeeks" , "geeks" , "geek" , "geezer" ,
"geekathon" };
int n = sizeof (arr) / sizeof (arr[0]);
struct Node* head = NULL;
// A linked list is created with all the characters
// of the first string
Initialise(&head, arr[0]);
// Process all the remaining strings to find the
// longest common prefix
for ( int i = 1; i < n; i++)
longestCommonPrefix(&head, arr[i]);
printLongestCommonPrefix(head);
} |
Java
// Java Program to find the longest common prefix // in an array of strings import java.util.Arrays;
public class Main {
// Structure for a node in the linked list
static class Node {
char data;
Node next;
}
// Function to print the data in the linked list
// Remaining nodes represent the longest common prefix
static void printLongestCommonPrefix(Node head)
{
// If the linked list is empty there is
// no common prefix
if (head == null ) {
System.out.println( "There is no common prefix" );
return ;
}
// Printing the longest common prefix
System.out.print( "The longest common prefix is " );
while (head != null ) {
System.out.print(head.data);
head = head.next;
}
System.out.println();
}
// Function that creates a linked list of characters
// for the first word in the array of strings
static void initialise(Node[] head, String str)
{
// we calculate the length of the string
// as we will insert from the last to the
// first character
int l = str.length();
// inserting all the nodes with the characters
// using insert at the beginning technique
for ( int i = l - 1 ; i >= 0 ; i--) {
Node temp = new Node();
temp.data = str.charAt(i);
temp.next = head[ 0 ];
head[ 0 ] = temp;
}
}
// Function to delete all the nodes
// from the unmatched node till the end of the
// linked list
static void deleteNodes(Node head)
{
// temp is used to facilitate the deletion of nodes
Node current = head;
Node next;
while (current != null ) {
next = current.next;
current = null ;
current = next;
}
}
// Function that compares the character of the string with
// the nodes of the linked list and deletes all nodes after
// the characters that do not match
static void longestCommonPrefix(Node[] head, String str)
{
int i = 0 ;
// Use the pointer to the previous node to
// delete the link between the unmatched node
// and its prev node
Node temp = head[ 0 ];
Node prev = head[ 0 ];
while (temp != null ) {
// If the current string finishes or if the
// the characters in the linked list do not match
// with the character at the corresponding position
// delete all the nodes after that.
if (i == str.length() || temp.data != str.charAt(i)) {
// If the first node does not match then there
// is no common prefix
if (temp == head[ 0 ]) {
head[ 0 ] = null ;
}
// Delete all the nodes starting from the
// unmatched node
else {
prev.next = null ;
deleteNodes(temp);
}
break ;
}
// If the character matches, move to next
// node and store the address of the current
// node in prev
prev = temp;
temp = temp.next;
i++;
}
}
public static void main(String[] args)
{
String[] arr = { "geeksforgeeks" , "geeks" , "geek" , "geezer" , "geekathon" };
int n = arr.length;
Node[] head = new Node[ 1 ];
// A linked list is created with all the characters
// of the first string
initialise(head, arr[ 0 ]);
// Process all the remaining strings to find the
// longest common prefix
for ( int i = 1 ; i < n; i++) {
longestCommonPrefix(head, arr[i]);
}
printLongestCommonPrefix(head[ 0 ]);
}
} |
Python3
# Python Program to find the longest common prefix # in an array of strings # Class for a node in the linked list class Node:
def __init__( self , data):
self .data = data
self . next = None
# Function to print the data in the linked list # Remaining nodes represent the longest common prefix def printLongestCommonPrefix(head):
# If the linked list is empty there is
# no common prefix
if head is None :
print ( "There is no common prefix" )
return
# Printing the longest common prefix
print ( "The longest common prefix is " , end = '')
while head is not None :
print (head.data, end = '')
head = head. next
print ()
# Function that creates a linked list of characters # for the first word in the array of strings def Initialise(head, string):
# We calculate the length of the string
# as we will insert from the last to the
# first character
l = len (string)
# Inserting all the nodes with the characters
# using insert at the beginning technique
for i in range (l - 1 , - 1 , - 1 ):
temp = Node(string[i])
temp. next = head[ 0 ]
head[ 0 ] = temp
# Function to delete all the nodes # from the unmatched node till the end of the # linked list def deleteNodes(head):
# temp is used to facilitate the deletion of nodes
current = head
while current is not None :
next = current. next
del current
current = next
# Function that compares the character of the string with # the nodes of the linked list and deletes all nodes after # the characters that do not match def longestCommonPrefix(head, string):
i = 0
# Use the pointer to the previous node to
# delete the link between the unmatched node
# and its prev node
temp = head[ 0 ]
prev = head[ 0 ]
while temp is not None :
# If the current string finishes or if the
# the characters in the linked list do not match
# with the character at the corresponding position
# delete all the nodes after that.
if i = = len (string) or temp.data ! = string[i]:
# If the first node does not match then there
# is no common prefix
if temp = = head[ 0 ]:
del temp
head[ 0 ] = None
# Delete all the nodes starting from the
# unmatched node
else :
prev. next = None
deleteNodes(temp)
break
# If the character matches, move to next
# node and store the address of the current
# node in prev
prev = temp
temp = temp. next
i + = 1
if __name__ = = "__main__" :
arr = [ "geeksforgeeks" , "geeks" , "geek" , "geezer" , "geekathon" ]
n = len (arr)
head = [ None ]
# A linked list is created with all the characters
# of the first string
Initialise(head, arr[ 0 ])
# Process all the remaining strings to find the
# longest common prefix
for i in range ( 1 , n):
longestCommonPrefix(head, arr[i])
printLongestCommonPrefix(head[ 0 ])
# This code is contributed by codebraxnzt |
C#
using System;
// Structure for a node in the linked list public class Node {
public char data;
public Node next;
} public class LongestCommon_Prefix {
// Function to print the data in the linked list
// Remaining nodes represent the longest common prefix
static void PrintLongestCommonPrefix(Node head) {
// If the linked list is empty there is
// no common prefix
if (head == null ) {
Console.WriteLine( "There is no common prefix" );
return ;
}
// Printing the longest common prefix
Console.Write( "The longest common prefix is " );
while (head != null ) {
Console.Write(head.data);
head = head.next;
}
Console.WriteLine();
}
// Function that creates a linked list of characters
// for the first word in the array of strings
static void Initialise( ref Node head, string str) {
// We calculate the length of the string
// as we will insert from the last to the
// first character
int l = str.Length;
// Inserting all the nodes with the characters
// using insert at the beginning technique
for ( int i = l - 1; i >= 0; i--) {
Node temp = new Node();
temp.data = str[i];
temp.next = head;
head = temp;
}
}
// Function to delete all the nodes
// from the unmatched node till the end of the
// linked list
static void DeleteNodes(Node head) {
// temp is used to facilitate the deletion of nodes
Node current = head;
Node next;
while (current != null ) {
next = current.next;
current = null ;
current = next;
}
}
// Function that compares the character of the string with
// the nodes of the linked list and deletes all nodes after
// the characters that do not match
static void LongestCommonPrefix( ref Node head, string str) {
int i = 0;
// Use the pointer to the previous node to
// delete the link between the unmatched node
// and its prev node
Node temp = head;
Node prev = head;
while (temp != null ) {
// If the current string finishes or if the
// the characters in the linked list do not match
// with the character at the corresponding position
// delete all the nodes after that.
if (i == str.Length || temp.data != str[i]) {
// If the first node does not match then there
// is no common prefix
if (temp == head) {
head = null ;
}
// Delete all the nodes starting from the
// unmatched node
else {
prev.next = null ;
DeleteNodes(temp);
}
break ;
}
// If the character matches, move to next
// node and store the address of the current
// node in prev
prev = temp;
temp = temp.next;
i++;
}
}
static void Main() {
string [] arr = { "geeksforgeeks" , "geeks" , "geek" , "geezer" , "geekathon" };
int n = arr.Length;
Node head = null ;
// A linked list is created with all the characters
// of the first string
Initialise( ref head, arr[0]);
// Process all the remaining strings
for ( int i = 1; i < n; i++)
LongestCommonPrefix( ref head, arr[i]);
PrintLongestCommonPrefix(head);
}
} |
Javascript
// JavaScript Program to find the longest common prefix // in an array of strings // Class for a node in the linked list class Node { constructor(data) {
this .data = data;
this .next = null ;
}
} // Function to print the data in the linked list // Remaining nodes represent the longest common prefix function printLongestCommonPrefix(head) {
// If the linked list is empty there is
// no common prefix
if (head == null ) {
console.log( "There is no common prefix" );
return ;
}
ans= "" ;
// Printing the longest common prefix
while (head != null ) {
ans = ans + head.data;
head = head.next;
}
console.log( "The longest common prefix is " + ans);
} // Function that creates a linked list of characters // for the first word in the array of strings function Initialise(head, string) {
// We calculate the length of the string
// as we will insert from the last to the
// first character
let l = string.length;
// Inserting all the nodes with the characters
// using insert at the beginning technique
for (let i = l-1; i >= 0; i--) {
let temp = new Node(string[i]);
temp.next = head[0];
head[0] = temp;
}
} // Function to delete all the nodes // from the unmatched node till the end of the // linked list function deleteNodes(head) {
// temp is used to facilitate the deletion of nodes
let current = head;
while (current != null ) {
let next = current.next;
delete current;
current = next;
}
} // Function that compares the character of the string with // the nodes of the linked list and deletes all nodes after // the characters that do not match function longestCommonPrefix(head, string) {
let i = 0;
// Use the pointer to the previous node to
// delete the link between the unmatched node
// and its prev node
let temp = head[0];
let prev = head[0];
while (temp != null ) {
// If the current string finishes or if the
// the characters in the linked list do not match
// with the character at the corresponding position
// delete all the nodes after that.
if (i == string.length || temp.data != string[i]) {
// If the first node does not match then there
// is no common prefix
if (temp == head[0]) {
delete temp;
head[0] = null ;
}
// Delete all the nodes starting from the
// unmatched node
else {
prev.next = null ;
deleteNodes(temp);
}
break ;
}
// If the character matches, move to next
// node and store the address of the current
// node in prev
prev = temp;
temp = temp.next;
i += 1;
}
} let arr = [ "geeksforgeeks" , "geeks" , "geek" , "geezer" , "geekathon" ];
let n = arr.length;
let head = [ null ];
// A linked list is created with all the characters
// of the first string
Initialise(head, arr[0]);
// Process all the remaining strings to find the
// longest common prefix
for (let i = 1; i < n; i++) {
longestCommonPrefix(head, arr[i]);
}
printLongestCommonPrefix(head[0]);
|
Output
The longest common prefix is gee
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