HackerRank Insert a node at the head of a linked list problem solution YASH PAL, 31 July 2024 In this HackerRank Insert a node at the head of a linked list problem we need to develop a program in which if we have given a head node pointer of a linked list and the value that we need to add to the list. so we need to create a new node and assign that value to the node and then we need to insert that node at the head of the linked list and then return the reference of a new head node of that linked list. Problem solution in Python programming. #!/bin/python3 import math import os import random import re import sys class SinglyLinkedListNode: def __init__(self, node_data): self.data = node_data self.next = None class SinglyLinkedList: def __init__(self): self.head = None self.tail = None def print_singly_linked_list(node, sep, fptr): while node: fptr.write(str(node.data)) node = node.next if node: fptr.write(sep) def insertNodeAtHead(llist, data): # Write your code here node = SinglyLinkedListNode(data) if llist: node.next = llist return node if __name__ == '__main__': fptr = open(os.environ['OUTPUT_PATH'], 'w') llist_count = int(input()) llist = SinglyLinkedList() for _ in range(llist_count): llist_item = int(input()) llist_head = insertNodeAtHead(llist.head, llist_item) llist.head = llist_head print_singly_linked_list(llist.head, 'n', fptr) fptr.write('n') fptr.close() Problem solution in Java Programming. import java.io.*; import java.math.*; import java.security.*; import java.text.*; import java.util.*; import java.util.concurrent.*; import java.util.regex.*; public class Solution { static class SinglyLinkedListNode { public int data; public SinglyLinkedListNode next; public SinglyLinkedListNode(int nodeData) { this.data = nodeData; this.next = null; } } static class SinglyLinkedList { public SinglyLinkedListNode head; public SinglyLinkedListNode tail; public SinglyLinkedList() { this.head = null; this.tail = null; } } public static void printSinglyLinkedList(SinglyLinkedListNode node, String sep, BufferedWriter bufferedWriter) throws IOException { while (node != null) { bufferedWriter.write(String.valueOf(node.data)); node = node.next; if (node != null) { bufferedWriter.write(sep); } } } static SinglyLinkedListNode insertNodeAtHead(SinglyLinkedListNode llist, int data) { SinglyLinkedListNode temp; if(llist == null){ llist = new SinglyLinkedListNode(data); return llist; } temp = new SinglyLinkedListNode(data); temp.next = llist; llist = temp; return llist; } private static final Scanner scanner = new Scanner(System.in); public static void main(String[] args) throws IOException { BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(System.getenv("OUTPUT_PATH"))); SinglyLinkedList llist = new SinglyLinkedList(); int llistCount = scanner.nextInt(); scanner.skip("(rn|[nru2028u2029u0085])?"); for (int i = 0; i < llistCount; i++) { int llistItem = scanner.nextInt(); scanner.skip("(rn|[nru2028u2029u0085])?"); SinglyLinkedListNode llist_head = insertNodeAtHead(llist.head, llistItem); llist.head = llist_head; } printSinglyLinkedList(llist.head, "n", bufferedWriter); bufferedWriter.newLine(); bufferedWriter.close(); scanner.close(); } } Problem solution in C++ programming. #include <bits/stdc++.h> using namespace std; class SinglyLinkedListNode { public: int data; SinglyLinkedListNode *next; SinglyLinkedListNode(int node_data) { this->data = node_data; this->next = nullptr; } }; class SinglyLinkedList { public: SinglyLinkedListNode *head; SinglyLinkedListNode *tail; SinglyLinkedList() { this->head = nullptr; this->tail = nullptr; } }; void print_singly_linked_list(SinglyLinkedListNode* node, string sep, ofstream& fout) { while (node) { fout << node->data; node = node->next; if (node) { fout << sep; } } } void free_singly_linked_list(SinglyLinkedListNode* node) { while (node) { SinglyLinkedListNode* temp = node; node = node->next; free(temp); } } SinglyLinkedListNode* insertNodeAtHead(SinglyLinkedListNode* llist, int data) { SinglyLinkedListNode *newN = new SinglyLinkedListNode(data); newN->next = llist; return newN; } int main() { ofstream fout(getenv("OUTPUT_PATH")); SinglyLinkedList* llist = new SinglyLinkedList(); int llist_count; cin >> llist_count; cin.ignore(numeric_limits<streamsize>::max(), 'n'); for (int i = 0; i < llist_count; i++) { int llist_item; cin >> llist_item; cin.ignore(numeric_limits<streamsize>::max(), 'n'); SinglyLinkedListNode* llist_head = insertNodeAtHead(llist->head, llist_item); llist->head = llist_head; } print_singly_linked_list(llist->head, "n", fout); fout << "n"; free_singly_linked_list(llist->head); fout.close(); return 0; } Problem solution in C programming. #include <assert.h> #include <limits.h> #include <math.h> #include <stdbool.h> #include <stddef.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <string.h> char* readline(); typedef struct SinglyLinkedListNode SinglyLinkedListNode; typedef struct SinglyLinkedList SinglyLinkedList; struct SinglyLinkedListNode { int data; SinglyLinkedListNode* next; }; struct SinglyLinkedList { SinglyLinkedListNode* head; SinglyLinkedListNode* tail; }; SinglyLinkedListNode* create_singly_linked_list_node(int node_data) { SinglyLinkedListNode* node = malloc(sizeof(SinglyLinkedListNode)); node->data = node_data; node->next = NULL; return node; } void print_singly_linked_list(SinglyLinkedListNode* node, char* sep, FILE* fptr) { while (node) { fprintf(fptr, "%d", node->data); node = node->next; if (node) { fprintf(fptr, "%s", sep); } } } void free_singly_linked_list(SinglyLinkedListNode* node) { while (node) { SinglyLinkedListNode* temp = node; node = node->next; free(temp); } } // Complete the insertNodeAtHead function below. /* * For your reference: * * SinglyLinkedListNode { * int data; * SinglyLinkedListNode* next; * }; * */ SinglyLinkedListNode* insertNodeAtHead(SinglyLinkedListNode* llist, int data) { SinglyLinkedListNode* newnode = create_singly_linked_list_node(data); newnode->next = llist; return newnode; } int main() { FILE* fptr = fopen(getenv("OUTPUT_PATH"), "w"); SinglyLinkedList* llist = malloc(sizeof(SinglyLinkedList)); llist->head = NULL; llist->tail = NULL; char* llist_count_endptr; char* llist_count_str = readline(); int llist_count = strtol(llist_count_str, &llist_count_endptr, 10); if (llist_count_endptr == llist_count_str || *llist_count_endptr != ' ') { exit(EXIT_FAILURE); } for (int i = 0; i < llist_count; i++) { char* llist_item_endptr; char* llist_item_str = readline(); int llist_item = strtol(llist_item_str, &llist_item_endptr, 10); if (llist_item_endptr == llist_item_str || *llist_item_endptr != ' ') { exit(EXIT_FAILURE); } SinglyLinkedListNode* llist_head = insertNodeAtHead(llist->head, llist_item); llist->head = llist_head; } char *sep = "n"; print_singly_linked_list(llist->head, sep, fptr); fprintf(fptr, "n"); free_singly_linked_list(llist->head); fclose(fptr); return 0; } char* readline() { size_t alloc_length = 1024; size_t data_length = 0; char* data = malloc(alloc_length); while (true) { char* cursor = data + data_length; char* line = fgets(cursor, alloc_length - data_length, stdin); if (!line) { break; } data_length += strlen(cursor); if (data_length < alloc_length - 1 || data[data_length - 1] == 'n') { break; } alloc_length <<= 1; data = realloc(data, alloc_length); if (!line) { break; } } if (data[data_length - 1] == 'n') { data[data_length - 1] = ' '; data = realloc(data, data_length); } else { data = realloc(data, data_length + 1); data[data_length] = ' '; } return data; } Problem solution in JavaScript programming. 'use strict'; const fs = require('fs'); process.stdin.resume(); process.stdin.setEncoding('utf-8'); let inputString = ''; let currentLine = 0; process.stdin.on('data', inputStdin => { inputString += inputStdin; }); process.stdin.on('end', function() { inputString = inputString.replace(/s*$/, '') .split('n') .map(str => str.replace(/s*$/, '')); main(); }); function readLine() { return inputString[currentLine++]; } const SinglyLinkedListNode = class { constructor(nodeData) { this.data = nodeData; this.next = null; } }; const SinglyLinkedList = class { constructor() { this.head = null; this.tail = null; } }; function printSinglyLinkedList(node, sep, ws) { while (node != null) { ws.write(String(node.data)); node = node.next; if (node != null) { ws.write(sep); } } } // Complete the insertNodeAtHead function below. /* * For your reference: * * SinglyLinkedListNode { * int data; * SinglyLinkedListNode next; * } * */ function insertNodeAtHead(head, data) { if(head == null){ return new SinglyLinkedListNode(data); } var node = new SinglyLinkedListNode(data); node.next = head; return node; } function main() { const ws = fs.createWriteStream(process.env.OUTPUT_PATH); const llistCount = parseInt(readLine(), 10); let llist = new SinglyLinkedList(); for (let i = 0; i < llistCount; i++) { const llistItem = parseInt(readLine(), 10); const llist_head = insertNodeAtHead(llist.head, llistItem); llist.head = llist_head; } printSinglyLinkedList(llist.head, 'n', ws); ws.write('n'); ws.end(); } coding problems data structure