Given a singly linked list containing n nodes. Modify the value of first half nodes such that 1st node’s new value is equal to the last node’s value minus first node’s current value, 2nd node’s new value is equal to the second last node’s value minus 2nd node’s current value, likewise for first half nodes. If n is odd then the value of the middle node remains unchanged.
Examples:
Input: 10 -> 4 -> 5 -> 3 -> 6
Output: -4 -> -1 -> 5 -> 3 -> 6Input: 2 -> 9 -> 8 -> 12 -> 7 -> 10
Output: 8 -> -2 -> 4 -> 12 -> 7 -> 10
Approach: Traverse the link list using recursion for only second half of the list rather than recursing the whole list, thereby reducing the stack frame. Based on the number of nodes in the list, we calculate the starting point for the second half of the list and the list is recursed for the second half. Once the second half is recursed completely, the value of the node present in the stack and the value of the current node is subtracted.
Below is the implementation of the above approach:
C++
// C++ program to modify the contents // of the linked list with recursion #include <bits/stdc++.h> using namespace std; // Represents a Node of the linked list struct Node { int data; Node* next; }; // Function to create and return a new node Node* insert( int data) { Node* temp; temp = new Node; temp->data = data; temp->next = NULL; return temp; } // Function which returns the total number of // node present in the list int getTotalNodeCount(Node* head) { int totalNodesCount = 0; while (head != NULL) { totalNodesCount++; head = head->next; } return totalNodesCount; } // Function to modify the contents // of the given linked lists void modifyContents(Node** first_half , Node* second_half) { if (second_half == NULL) { return ; } modifyContents(first_half,second_half->next); (*first_half)->data = second_half->data - (*first_half)->data; (*first_half) = (*first_half)->next; return ; } // Wrapper function which calculates the starting // point for second half of the list void modifyContentsWrapper(Node** head) { Node *ptr = NULL; // pointer to second half of list Node *temp = NULL; int diff = 0; int length = 0; // number of nodes in the list if (*head == NULL) { return ; } length = getTotalNodeCount(*head); // If link list has odd number of nodes, then pointer // for second half starts from (length of link list + 1). // Say for an example, for the list 10->4->5->3->6 pointer // should start from 3. // If list has even number of nodes, 10->4->5->9->6->8, // pointer starts from 9. diff = (length%2 == 0? (length/2) :(length/2)+1 ); ptr = *head; while (diff--) ptr = ptr->next; temp = *head; modifyContents(&temp,ptr); return ; } // Function to print the contents of the linked list void print(Node* nod) { if (nod == NULL) { return ; } cout << nod->data; if (nod->next != NULL) cout << " -> " ; print(nod->next); } // Driver code int main() { Node* head = insert(2); head->next = insert(9); head->next->next = insert(8); head->next->next->next = insert(12); head->next->next->next->next = insert(7); head->next->next->next->next->next = insert(10); // Modify the linked list modifyContentsWrapper(&head); // Print the modified linked list print(head); return 0; } |
Java
// Java program to modify the contents // of the linked list with recursion class GFG { // Represents a Node of the linked list static class Node { int data; Node next; }; // Function to create and return a new node static Node insert( int data) { Node temp; temp = new Node(); temp.data = data; temp.next = null ; return temp; } // Function which returns the total number // of node present in the list static int getTotalNodeCount(Node head) { int totalNodesCount = 0 ; while (head != null ) { totalNodesCount++; head = head.next; } return totalNodesCount; } static Node temp = null ; // Function to modify the contents // of the given linked lists static void modifyContents(Node second_half) { if (second_half == null ) { return ; } modifyContents(second_half.next); (temp).data = second_half.data - (temp).data; (temp) = (temp).next; return ; } // Wrapper function which calculates the starting // point for second half of the list static Node modifyContentsWrapper(Node head) { Node ptr = null ; // pointer to second half of list temp = null ; int diff = 0 ; int length = 0 ; // number of nodes in the list if (head == null ) { return null ; } length = getTotalNodeCount(head); // If link list has odd number of nodes, // then pointer for second half starts // from (length of link list + 1). // Say for an example, for the list 10.4.5.3.6 // pointer should start from 3. // If list has even number of nodes, // 10.4.5.9.6.8, pointer starts from 9. diff = (length % 2 == 0 ? (length / 2 ) : (length / 2 ) + 1 ); ptr = head; while (diff--> 0 ) ptr = ptr.next; temp = head; modifyContents(ptr); return head; } // Function to print the contents // of the linked list static void print(Node nod) { if (nod == null ) { return ; } System.out.print( nod.data); if (nod.next != null ) System.out.print( " -> " ); print(nod.next); } // Driver code public static void main(String args[]) { Node head = insert( 2 ); head.next = insert( 9 ); head.next.next = insert( 8 ); head.next.next.next = insert( 12 ); head.next.next.next.next = insert( 7 ); head.next.next.next.next.next = insert( 10 ); // Modify the linked list head = modifyContentsWrapper(head); // Print the modified linked list print(head); } } // This code is contributed by Arnab Kundu |
Python
# Python program to modify the contents # of the linked list with recursion # Represents a Node of the linked list class Node: def __init__( self , data): self .data = data self . next = None # Function to create and return a new node def insert( data) : temp = Node( 0 ) temp.data = data temp. next = None return temp # Function which returns the total number # of node present in the list def getTotalNodeCount( head) : totalNodesCount = 0 while (head ! = None ): totalNodesCount = totalNodesCount + 1 head = head. next return totalNodesCount temp = None # Function to modify the contents # of the given linked lists def modifyContents( second_half) : if (second_half = = None ): return global temp modifyContents(second_half. next ) (temp).data = second_half.data - (temp).data (temp) = (temp). next return # Wrapper function which calculates the starting # point for second half of the list def modifyContentsWrapper(head) : # pointer to second half of list ptr = None diff = 0 # number of nodes in the list length = 0 global temp temp = None if (head = = None ) : return None length = getTotalNodeCount(head) # If link list has odd number of nodes, # then pointer for second half starts # from (length of link list + 1). # Say for an example, for the list 10.4.5.3.6 # pointer should start from 3. # If list has even number of nodes, # 10.4.5.9.6.8, pointer starts from 9. if (length % 2 = = 0 ): diff = (length / 2 ) else : diff = (length / 2 ) + 1 ptr = head while (diff > 0 ): diff = diff - 1 ptr = ptr. next temp = head modifyContents(ptr) return head # Function to print the contents # of the linked list def print_(nod): if (nod = = None ) : return print (nod.data, end = " " ) if (nod. next ! = None ): print ( " -> " ,end = "") print_(nod. next ) # Driver code head = insert( 2 ) head. next = insert( 9 ) head. next . next = insert( 8 ) head. next . next . next = insert( 12 ) head. next . next . next . next = insert( 7 ) head. next . next . next . next . next = insert( 10 ) # Modify the linked list head = modifyContentsWrapper(head) # Print the modified linked list print_(head) # This code is contributed by Arnab Kundu |
C#
// C# program to modify the contents // of the linked list with recursion using System; class GFG { // Represents a Node of the linked list public class Node { public int data; public Node next; }; // Function to create and return a new node static Node insert( int data) { Node temp; temp = new Node(); temp.data = data; temp.next = null ; return temp; } // Function which returns the total number // of node present in the list static int getTotalNodeCount(Node head) { int totalNodesCount = 0; while (head != null ) { totalNodesCount++; head = head.next; } return totalNodesCount; } static Node temp = null ; // Function to modify the contents // of the given linked lists static void modifyContents(Node second_half) { if (second_half == null ) { return ; } modifyContents(second_half.next); (temp).data = second_half.data - (temp).data; (temp) = (temp).next; return ; } // Wrapper function which calculates the starting // point for second half of the list static Node modifyContentsWrapper(Node head) { // pointer to second half of list Node ptr = null ; temp = null ; int diff = 0; // number of nodes in the list int length = 0; if (head == null ) { return null ; } length = getTotalNodeCount(head); // If link list has odd number of nodes, // then pointer for second half starts // from (length of link list + 1). // Say for an example, for the list 10.4.5.3.6 // pointer should start from 3. // If list has even number of nodes, // 10.4.5.9.6.8, pointer starts from 9. diff = (length % 2 == 0 ? (length / 2) : (length / 2) + 1); ptr = head; while (diff-->0) ptr = ptr.next; temp = head; modifyContents(ptr); return head; } // Function to print the contents // of the linked list static void print(Node nod) { if (nod == null ) { return ; } Console.Write(nod.data); if (nod.next != null ) Console.Write( " -> " ); print(nod.next); } // Driver code public static void Main(String []args) { Node head = insert(2); head.next = insert(9); head.next.next = insert(8); head.next.next.next = insert(12); head.next.next.next.next = insert(7); head.next.next.next.next.next = insert(10); // Modify the linked list head = modifyContentsWrapper(head); // Print the modified linked list print(head); } } // This code is contributed by PrinciRaj1992 |
Javascript
<script> // JavaScript program to modify the contents // of the linked list with recursion // Represents a Node of the linked list class Node { constructor() { this .data = 0; this .next = null ; } } // Function to create and return a new node function insert(data) { var temp; temp = new Node(); temp.data = data; temp.next = null ; return temp; } // Function which returns the total number // of node present in the list function getTotalNodeCount(head) { var totalNodesCount = 0; while (head != null ) { totalNodesCount++; head = head.next; } return totalNodesCount; } var temp = null ; // Function to modify the contents // of the given linked lists function modifyContents(second_half) { if (second_half == null ) { return ; } modifyContents(second_half.next); temp.data = second_half.data - temp.data; temp = temp.next; return ; } // Wrapper function which calculates the starting // point for second half of the list function modifyContentsWrapper(head) { // pointer to second half of list var ptr = null ; temp = null ; var diff = 0; // number of nodes in the list var length = 0; if (head == null ) { return null ; } length = getTotalNodeCount(head); // If link list has odd number of nodes, // then pointer for second half starts // from (length of link list + 1). // Say for an example, for the list 10.4.5.3.6 // pointer should start from 3. // If list has even number of nodes, // 10.4.5.9.6.8, pointer starts from 9. diff = length % 2 == 0 ? parseInt(length / 2) : parseInt(length / 2) + 1; ptr = head; while (diff-- > 0) ptr = ptr.next; temp = head; modifyContents(ptr); return head; } // Function to print the contents // of the linked list function print(nod) { if (nod == null ) { return ; } document.write(nod.data); if (nod.next != null ) document.write( " -> " ); print(nod.next); } // Driver code var head = insert(2); head.next = insert(9); head.next.next = insert(8); head.next.next.next = insert(12); head.next.next.next.next = insert(7); head.next.next.next.next.next = insert(10); // Modify the linked list head = modifyContentsWrapper(head); // Print the modified linked list print(head); </script> |
8 -> -2 -> 4 -> 12 -> 7 -> 10
Complexity Analysis:
- Time Complexity: O(N), as we are using recursive calls to traverse N times, where N is the number of Nodes in the linked list.
- Auxiliary Space: O(1), as we are not using any extra space.
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