Algorithm
Problem Name: Data Structures -
In this HackerRank in Data Structures -
Given a pointer to the head of a linked list, insert a new node before the head. The next value in the new node should point to head and the data value should be replaced with a given value. Return a reference to the new head of the list. The head pointer given may be null meaning that the initial list is empty.
Function Description
Complete the function insertNodeAtHead in the editor below.
insertNodeAtHead has the following parameter(s):
- SinglyLinkedListNode llist: a reference to the head of a list
- data: the value to insert in the data field of the new node
Input Format
The first line contains an integer
, the number of elements to be inserted at the head of the list.
The next n lines contain an integer each, the elements to be inserted, one per function call.
Constraints
- 1 <= n <=1000
- 1 <= list[i] <= 1000
Sample Input
5
383
484
392
975
321
Sample Output
321
975
392
484
383
Explanation
Intially the list in NULL. After inserting 383, the list is 383 -> NULL.
After inserting 484, the list is 484 -> 383 -> NULL.
After inserting 392, the list is 392 -> 484 -> 383 -> NULL.
After inserting 975, the list is 975 -> 392 -> 484 -> 383 -> NULL.
After inserting 321, the list is 321 -> 975 -> 392 -> 484 -> 383 -> NULL.
Code Examples
#1 Code Example with C Programming
Code -
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 != '\0') { 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 != '\0') { 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] = '\0';
data = realloc(data, data_length);
} else {
data = realloc(data, data_length + 1);
data[data_length] = '\0';
}
return data;
}
#2 Code Example with C++ Programming
Code -
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;
}
#3 Code Example with Java Programming
Code -
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("(\r\n|[\n\r\u2028\u2029\u0085])?");
for (int i = 0; i < llistCount; i++) {
int llistItem = scanner.nextInt();
scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
SinglyLinkedListNode llist_head = insertNodeAtHead(llist.head, llistItem);
llist.head = llist_head;
}
printSinglyLinkedList(llist.head, "\n", bufferedWriter);
bufferedWriter.newLine();
bufferedWriter.close();
scanner.close(>;
}
}
#4 Code Example with Javascript Programming
Code -
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(>;
}
#5 Code Example with Python Programming
Code -
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)
# Complete the insertNodeAtHead function below.
#
# For your reference:
#
# SinglyLinkedListNode:
# int data
# SinglyLinkedListNode next
#
#
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()