Reverse nodes of a linked list without affecting the special characters

Last Updated : 27 Mar, 2023

Given a linked list of alphabets and special characters. Reverse the given linked list without affecting the position of the special characters.

Examples:

Input: g -> @ -> e -> # -> e -> $ -> k -> s -> NULL
Output: s -> @ -> k -> # -> e -> $ -> e -> g -> NULL
Explanation: Here we can see that in the output the position of special character in not change and also linked list is reverse.

The idea is to traverse the linked list and store the characters excluding the special characters in a temporary array. Again traverse the linked list and copy elements from the array to the nodes of the linked list in a reverse manner.

Below is the step by step algorithm:

Take a temporary array, TEMP_ARR.
Traverse the linked list and do the following
- if the current element is an alphabet, store that element of the linked list to TEMP_ARR.
- else, increase node pointer by one
Again traverse the linked list from the head and TEMP_ARR from the end and do the following:
- if the current element is an alphabet, copy the last element of TEMP_ARR to the current linked list node and decrease the current index of TEMP_ARR for the next iteration.
- else, increase node by one

Below is the implementation of above approach:

C++

// C++ program to reverse a linked list // without affecting special characters  #include <iostream>  using namespace std;  // Link list node  struct Node {     char data;     struct Node* next; };  // Function to reverse the linked list // without affecting special characters void reverse(struct Node** head_ref, int size) {     struct Node* current = *head_ref;               char TEMP_ARR[size];          int i = 0;          // Traverse the linked list and insert     // linked list elements to TEMP_ARR     while (current != NULL) {         // if the current data is any alphabet than         // store it in to TEMP_ARR         if ((current->data >= 97 && current->data <= 122) ||                  (current->data >= 65 && current->data <= 90)) {             TEMP_ARR[i++] = current->data;             current = current->next;         }         // else increase the node position         else             current = current->next;     }          current = *head_ref;     // Traverse the linked list again     while (current != NULL)      {         // if current character is an alphabet than         // replace the current element in the linked list         // with the last element of the TEMP_ARR         if ((current->data >= 97 && current->data <= 122) ||                  (current->data >= 65 && current->data <= 90)) {             current->data = TEMP_ARR[--i];             current = current->next;         }         // else increase the node         else             current = current->next;     } }  // Function to push a node  void push(struct Node** head_ref, char new_data) {     /* allocate node */     struct Node* new_node = new Node();      /* put in the data */     new_node->data = new_data;      /* link the old list of the new node */     new_node->next = (*head_ref);      /* move the head to point to the new node */     (*head_ref) = new_node; }  /* Function to print linked list */ void printList(struct Node* head) {     struct Node* temp = head;     while (temp != NULL) {         cout << temp->data;         temp = temp->next;     } }  // Driver program to test above function int main() {     /* Start with the empty list */     struct Node* head = NULL;      push(&head, 's');     push(&head, '$');     push(&head, 'k');     push(&head, 'e');     push(&head, 'e');     push(&head, '@');     push(&head, '#');     push(&head, 'g');     push(&head, 'r');     push(&head, 'o');     push(&head, 'f');     push(&head, 's');     push(&head, '$');     push(&head, 'k');     push(&head, 'e');     push(&head, 'e');     push(&head, 'g');      cout << "Given linked list: ";     printList(head);          reverse(&head, 13);          cout << "\nReversed Linked list: ";     printList(head);          return 0; }

Java

// Java program to reverse a  // linked list without affecting  // special characters class GFG {  // Link list node  public static class Node  {     char data;     Node next; }  // Function to reverse the linked // list without affecting special  // characters static void reverse(Node head_ref,                     int size) { Node current = head_ref;   char TEMP_ARR[] = new char[size];  int i = 0;  // Traverse the linked list  // and insert linked list  // elements to TEMP_ARR while (current != null) {     // if the current data      // is any alphabet than     // store it in to TEMP_ARR     if ((current.data >= 97 &&           current.data <= 122) ||          (current.data >= 65 &&           current.data <= 90))     {         TEMP_ARR[i++] = current.data;         current = current.next;     }          // else increase the node position     else         current = current.next; }  current = head_ref;  // Traverse the linked list again while (current != null)  {     // if current character is an      // alphabet than replace the      // current element in the linked     // list with the last element      // of the TEMP_ARR     if ((current.data >= 97 &&           current.data <= 122) ||          (current.data >= 65 &&           current.data <= 90))      {         current.data = TEMP_ARR[--i];         current = current.next;     }          // else increase the node     else         current = current.next;     } }  // Function to push a node  static Node push(Node head_ref,                  char new_data) {     /* allocate node */     Node new_node = new Node();      /* put in the data */     new_node.data = new_data;      /* link the old list        off the new node */     new_node.next = (head_ref);      /* move the head to point         to the new node */     (head_ref) = new_node;          return head_ref; }  /* Function to print linked list */ static void printList(Node head) {     Node temp = head;     while (temp != null)      {         System.out.print(temp.data);         temp = temp.next;     } }  // Driver Code public static void main(String rags[]) {     /* Start with the empty list */     Node head = null;      head = push(head, 's');     head = push(head, '$');     head = push(head, 'k');     head = push(head, 'e');     head = push(head, 'e');     head = push(head, '@');     head = push(head, '#');     head = push(head, 'g');     head = push(head, 'r');     head = push(head, 'o');     head = push(head, 'f');     head = push(head, 's');     head = push(head, '$');     head = push(head, 'k');     head = push(head, 'e');     head = push(head, 'e');     head = push(head, 'g');      System.out.print( "Given linked list: ");     printList(head);          reverse(head, 13);          System.out.print("\nReversed Linked list: ");     printList(head); } }  // This code is contributed by Arnab Kundu

Python3

# Python3 program to reverse a linked list # without affecting special characters  # Link list node class Node:          def __init__(self, x):                  self.data = x         self.next = None  # Function to reverse the linked list # without affecting special characters def reverse(head_ref, size):          current = head_ref     TEMP_ARR = [0 for i in range(256)]      i = 0      # Traverse the linked list and insert     # linked list elements to TEMP_ARR     while (current != None):                  # If the current data is any alphabet than         # store it in to TEMP_ARR         if ((ord(current.data) >= 97 and               ord(current.data) <= 122) or             (ord(current.data) >= 65 and               ord(current.data) <= 90)):             TEMP_ARR[i]= current.data             i += 1             current = current.next                      # Else increase the node position         else:             current = current.next      current = head_ref          # Traverse the linked list again     while (current != None):                  # If current character is an alphabet         # than replace the current element in          # the linked list with the last element         # of the TEMP_ARR         if ((ord(current.data) >= 97 and              ord(current.data) <= 122) or              (ord(current.data) >= 65 and               ord(current.data) <= 90)):             i = i - 1             current.data = TEMP_ARR[i]             current = current.next                      # Else increase the node         else:             current = current.next                  return head_ref  # Function to push a node def push(head_ref, new_data):          # Allocate node      #new_node = (struct Node*)malloc(sizeof(struct Node));      # Put in the data      new_node = Node(new_data)      # Link the old list of the new node      new_node.next = head_ref      # Move the head to point to the new node      head_ref = new_node      return head_ref  # Function to print linked list  def printList(head):          temp = head          while (temp != None):         print(temp.data, end = "")         temp = temp.next  # Driver code if __name__ == '__main__':          # Start with the empty list      head = None      head = push(head, 's')     head = push(head, '$')     head = push(head, 'k')     head = push(head, 'e')     head = push(head, 'e')     head = push(head, '@')     head = push(head, '#')     head = push(head, 'g')     head = push(head, 'r')     head = push(head, 'o')     head = push(head, 'f')     head = push(head, 's')     head = push(head, '$')     head = push(head, 'k')     head = push(head, 'e')     head = push(head, 'e')     head = push(head, 'g')      print("Given linked list: ", end = "")     printList(head)      head = reverse(head, 13)      print("\nReversed Linked list: ", end = "")     printList(head)  # This code is contributed by mohit kumar 29

// C# program to reverse a  // linked list without affecting  // special characters using System;  class GFG {      // Link list node      public class Node      {         public char data;         public Node next;     }      // Function to reverse the linked     // list without affecting special      // characters     static void reverse(Node head_ref,                         int size)     {         Node current = head_ref;          char []TEMP_ARR = new char[size];          int i = 0;          // Traverse the linked list          // and insert linked list          // elements to TEMP_ARR         while (current != null)         {             // if the current data              // is any alphabet than             // store it in to TEMP_ARR             if ((current.data >= 97 &&                  current.data <= 122) ||                  (current.data >= 65 &&                  current.data <= 90))             {                 TEMP_ARR[i++] = current.data;                 current = current.next;             }              // else increase the node position             else                 current = current.next;         }          current = head_ref;          // Traverse the linked list again         while (current != null)          {             // if current character is an              // alphabet than replace the              // current element in the linked             // list with the last element               // of the TEMP_ARR             if ((current.data >= 97 &&                  current.data <= 122) ||                  (current.data >= 65 &&                  current.data <= 90))              {                 current.data = TEMP_ARR[--i];                 current = current.next;             }              // else increase the node             else                 current = current.next;         }     }      // Function to push a node      static Node push(Node head_ref,                     char new_data)     {         /* allocate node */         Node new_node = new Node();          /* put in the data */         new_node.data = new_data;          /* link the old list         off the new node */         new_node.next = (head_ref);          /* move the head to point          to the new node */         (head_ref) = new_node;          return head_ref;     }      /* Function to print linked list */     static void printList(Node head)     {         Node temp = head;         while (temp != null)          {             Console.Write(temp.data);             temp = temp.next;         }     }      // Driver Code     public static void Main(String []rags)     {         /* Start with the empty list */         Node head = null;          head = push(head, 's');         head = push(head, '$');         head = push(head, 'k');         head = push(head, 'e');         head = push(head, 'e');         head = push(head, '@');         head = push(head, '#');         head = push(head, 'g');         head = push(head, 'r');         head = push(head, 'o');         head = push(head, 'f');         head = push(head, 's');         head = push(head, '$');         head = push(head, 'k');         head = push(head, 'e');         head = push(head, 'e');         head = push(head, 'g');          Console.Write( "Given linked list: ");         printList(head);          reverse(head, 13);          Console.Write("\nReversed Linked list: ");         printList(head);     } }  // This code has been contributed  // by 29AjayKumar

JavaScript

<script>  // JavaScript program to reverse a // linked list without affecting // special characters  // Link list node class Node {     constructor()     {         let data,next;     } }  // Function to reverse the linked // list without affecting special // characters function reverse(head_ref,size) {     let current = head_ref;     let TEMP_ARR = new Array(size);   let i = 0;   // Traverse the linked list // and insert linked list // elements to TEMP_ARR while (current != null) {     // if the current data     // is any alphabet than     // store it in to TEMP_ARR     if ((current.data.charCodeAt(0) >= 97 &&          current.data.charCodeAt(0) <= 122) ||         (current.data.charCodeAt(0) >= 65 &&          current.data.charCodeAt(0) <= 90))     {         TEMP_ARR[i++] = current.data;         current = current.next;     }           // else increase the node position     else         current = current.next; }   current = head_ref;   // Traverse the linked list again while (current != null) {     // if current character is an     // alphabet than replace the     // current element in the linked     // list with the last element     // of the TEMP_ARR     if ((current.data.charCodeAt(0) >= 97 &&          current.data.charCodeAt(0) <= 122) ||         (current.data.charCodeAt(0) >= 65 &&          current.data.charCodeAt(0) <= 90))     {         current.data = TEMP_ARR[--i];         current = current.next;     }           // else increase the node     else         current = current.next; } return head_ref;      } // Function to push a node function push(head_ref,new_data) {     /* allocate node */     let new_node = new Node();       /* put in the data */     new_node.data = new_data;       /* link the old list        off the new node */     new_node.next = (head_ref);       /* move the head to point        to the new node */     (head_ref) = new_node;           return head_ref; }  /* Function to print linked list */ function printList(head) {     let temp = head;     while (temp != null)     {         document.write(temp.data);         temp = temp.next;     } }  // Driver Code  /* Start with the empty list */ let head = null;  head = push(head, 's'); head = push(head, '$'); head = push(head, 'k'); head = push(head, 'e'); head = push(head, 'e'); head = push(head, '@'); head = push(head, '#'); head = push(head, 'g'); head = push(head, 'r'); head = push(head, 'o'); head = push(head, 'f'); head = push(head, 's'); head = push(head, '$'); head = push(head, 'k'); head = push(head, 'e'); head = push(head, 'e'); head = push(head, 'g');  document.write( "Given linked list: "); printList(head);  head=reverse(head, 13);  document.write("<br>Reversed Linked list: "); printList(head);           // This code is contributed by unknown2108  </script>

Output

Given linked list: geek$sforg#@eek$s Reversed Linked list: skee$grofs#@kee$g

Complexity Analysis:

Time Complexity : O(N), where N is the total number of nodes in the linked list.
Auxiliary Space: O(N)

Print reverse of a Linked List without extra space and modifications

Shahnawaz_Ali

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Reverse nodes of a linked list without affecting the special characters

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