Algorithm

Problem Name: Data Structures - Insert a node at the head of a linked list

In this HackerRank in Data Structures - Insert a node at the head of a linked list solutions

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.

• 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>

int data;
};

};

node->data = node_data;
node->next = NULL;

return node;
}

while (node) {
fprintf(fptr, "%d", node->data);

node = node->next;

if (node) {
fprintf(fptr, "%s", sep);
}
}
}

while (node) {
node = node->next;

free(temp);
}
}

// Complete the insertNodeAtHead function below.

/*
*
*     int data;
* };
*
*/

newnode->next = llist;
return newnode;
}

int main()
{
FILE* fptr = fopen(getenv("OUTPUT_PATH"), "w");

llist->tail = NULL;

char* llist_count_endptr;
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;
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); }

}

char *sep = "\n";

fprintf(fptr, "\n");

fclose(fptr);

return 0;
}

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;
}

Copy The Code &

#2 Code Example with C++ Programming

Code - C++ Programming


#include <bits/stdc++.h>

using namespace std;

public:
int data;

this->data = node_data;
this->next = nullptr;
}
};

public:

this->tail = nullptr;
}

};

while (node) {
fout << node->data;

node = node->next;

if (node) {
fout << sep;
}
}
}

while (node) {
node = node->next;

free(temp);
}
}

newN->next = llist;
return newN;

}

int main()
{
ofstream fout(getenv("OUTPUT_PATH"));

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');

}

fout << "\n";

fout.close();

return 0;
}

Copy The Code &

#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 {

public int data;

this.data = nodeData;
this.next = 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);
}
}
}

if(llist == null){
return llist;
}
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")));

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])?");

}

bufferedWriter.newLine();

bufferedWriter.close();

scanner.close(>;
}
}

Copy The Code &

#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();
});

return inputString[currentLine++];
}

constructor(nodeData) {
this.data = nodeData;
this.next = null;
}
};

constructor() {
this.tail = null;
}

};

while (node != null) {
ws.write(String(node.data));

node = node.next;

if (node != null) {
ws.write(sep);
}
}
}

// Complete the insertNodeAtHead function below.

/*
*
*     int data;
* }
*
*/
}
return node;
}

function main() {
const ws = fs.createWriteStream(process.env.OUTPUT_PATH);

for (let i = 0; i < llistCount; i++) {
}

ws.write('\n');

ws.end(>;
}

Copy The Code &

#5 Code Example with Python Programming

Code - Python Programming


#!/bin/python3

import math
import os
import random
import re
import sys

def __init__(self, node_data):
self.data = node_data
self.next = None

def __init__(self):
self.tail = None

while node:
fptr.write(str(node.data))

node = node.next

if node:
fptr.write(sep)

# Complete the insertNodeAtHead function below.

#
#
#     int data
#
#
if llist:
node.next = llist
return node

if __name__ == '__main__':
fptr = open(os.environ['OUTPUT_PATH'], 'w')

llist_count = int(input())

for _ in range(llist_count):
llist_item = int(input())