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Reverse a doubly linked list – HackerRank Solution Java , Python 3, Python 2 , C , C++, Best and Optimal Solutions , All you need.
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C++ Reverse a doubly linked list HackerRank Solution
#include <bits/stdc++.h>
using namespace std;
class DoublyLinkedListNode {
public:
int data;
DoublyLinkedListNode *next;
DoublyLinkedListNode *prev;
DoublyLinkedListNode(int node_data) {
this->data = node_data;
this->next = nullptr;
this->prev = nullptr;
}
};
class DoublyLinkedList {
public:
DoublyLinkedListNode *head;
DoublyLinkedListNode *tail;
DoublyLinkedList() {
this->head = nullptr;
this->tail = nullptr;
}
void insert_node(int node_data) {
DoublyLinkedListNode* node = new DoublyLinkedListNode(node_data);
if (!this->head) {
this->head = node;
} else {
this->tail->next = node;
node->prev = this->tail;
}
this->tail = node;
}
};
void print_doubly_linked_list(DoublyLinkedListNode* node, string sep, ofstream& fout) {
while (node) {
fout << node->data;
node = node->next;
if (node) {
fout << sep;
}
}
}
void free_doubly_linked_list(DoublyLinkedListNode* node) {
while (node) {
DoublyLinkedListNode* temp = node;
node = node->next;
free(temp);
}
}
// Complete the reverse function below.
/*
* For your reference:
*
* DoublyLinkedListNode {
* int data;
* DoublyLinkedListNode* next;
* DoublyLinkedListNode* prev;
* };
*
*/
DoublyLinkedListNode* reverse(DoublyLinkedListNode* head)
{
// Complete this function
// Do not write the main method.
DoublyLinkedListNode *current = head;
DoublyLinkedListNode *temp = NULL;
while ( current != NULL) {
temp = current -> prev;
current -> prev = current -> next;
current -> next = temp;
current = current -> prev;
}
if (temp != NULL)
head = temp -> prev;
return head;
}
int main()
{
ofstream fout(getenv("OUTPUT_PATH"));
int t;
cin >> t;
cin.ignore(numeric_limits<streamsize>::max(), '\n');
for (int t_itr = 0; t_itr < t; t_itr++) {
DoublyLinkedList* llist = new DoublyLinkedList();
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');
llist->insert_node(llist_item);
}
DoublyLinkedListNode* llist1 = reverse(llist->head);
print_doubly_linked_list(llist1, " ", fout);
fout << "\n";
free_doubly_linked_list(llist1);
}
fout.close();
return 0;
}
Java Reverse a doubly linked list HackerRank Solution
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 DoublyLinkedListNode {
public int data;
public DoublyLinkedListNode next;
public DoublyLinkedListNode prev;
public DoublyLinkedListNode(int nodeData) {
this.data = nodeData;
this.next = null;
this.prev = null;
}
}
static class DoublyLinkedList {
public DoublyLinkedListNode head;
public DoublyLinkedListNode tail;
public DoublyLinkedList() {
this.head = null;
this.tail = null;
}
public void insertNode(int nodeData) {
DoublyLinkedListNode node = new DoublyLinkedListNode(nodeData);
if (this.head == null) {
this.head = node;
} else {
this.tail.next = node;
node.prev = this.tail;
}
this.tail = node;
}
}
public static void printDoublyLinkedList(DoublyLinkedListNode 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);
}
}
}
// Complete the reverse function below.
/*
* For your reference:
*
* DoublyLinkedListNode {
* int data;
* DoublyLinkedListNode next;
* DoublyLinkedListNode prev;
* }
*
*/
static DoublyLinkedListNode reverse(DoublyLinkedListNode curr) {
DoublyLinkedListNode temp = curr.next;
curr.next = curr.prev;
curr.prev = temp;
return temp == null ? curr : reverse(temp);
}
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 t = scanner.nextInt();
scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");
for (int tItr = 0; tItr < t; tItr++) {
DoublyLinkedList llist = new DoublyLinkedList();
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])?");
llist.insertNode(llistItem);
}
DoublyLinkedListNode llist1 = reverse(llist.head);
printDoublyLinkedList(llist1, " ", bufferedWriter);
bufferedWriter.newLine();
}
bufferedWriter.close();
scanner.close();
}
}
Python 3 Reverse a doubly linked list HackerRank Solution
#!/bin/python3
import math
import os
import random
import re
import sys
class DoublyLinkedListNode:
def __init__(self, node_data):
self.data = node_data
self.next = None
self.prev = None
class DoublyLinkedList:
def __init__(self):
self.head = None
self.tail = None
def insert_node(self, node_data):
node = DoublyLinkedListNode(node_data)
if not self.head:
self.head = node
else:
self.tail.next = node
node.prev = self.tail
self.tail = node
def print_doubly_linked_list(node, sep, fptr):
while node:
fptr.write(str(node.data))
node = node.next
if node:
fptr.write(sep)
# Complete the reverse function below.
#
# For your reference:
#
# DoublyLinkedListNode:
# int data
# DoublyLinkedListNode next
# DoublyLinkedListNode prev
#
#
def reverse(head):
if head == None or head.next == None:
return head
while True:
temp = head.next
head.next = head.prev
head.prev = temp
head = head.prev
if head.next == None:
break
temp = head.next
head.next = head.prev
head.prev = temp
return head
if __name__ == '__main__':
fptr = open(os.environ['OUTPUT_PATH'], 'w')
t = int(input())
for t_itr in range(t):
llist_count = int(input())
llist = DoublyLinkedList()
for _ in range(llist_count):
llist_item = int(input())
llist.insert_node(llist_item)
llist1 = reverse(llist.head)
print_doubly_linked_list(llist1, ' ', fptr)
fptr.write('\n')
fptr.close()
JavaScript Reverse a doubly linked list HackerRank Solution
'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', _ => {
inputString = inputString.replace(/\s*$/, '')
.split('\n')
.map(str => str.replace(/\s*$/, ''));
main();
});
function readLine() {
return inputString[currentLine++];
}
const DoublyLinkedListNode = class {
constructor(nodeData) {
this.data = nodeData;
this.next = null;
this.prev = null;
}
};
const DoublyLinkedList = class {
constructor() {
this.head = null;
this.tail = null;
}
insertNode(nodeData) {
let node = new DoublyLinkedListNode(nodeData);
if (this.head == null) {
this.head = node;
} else {
this.tail.next = node;
node.prev = this.tail;
}
this.tail = node;
}
};
function printDoublyLinkedList(node, sep, ws) {
while (node != null) {
ws.write(String(node.data));
node = node.next;
if (node != null) {
ws.write(sep);
}
}
}
// Complete the reverse function below.
/*
* For your reference:
*
* DoublyLinkedListNode {
* int data;
* DoublyLinkedListNode next;
* DoublyLinkedListNode prev;
* }
*
*/
function reverse(head) {
var current = head;
while(current) {
var curNext = current.next;
current.next = current.prev;
current.prev = curNext;
if (curNext) {
current = curNext;
}
else {
return current;
}
}
}
function main() {
const ws = fs.createWriteStream(process.env.OUTPUT_PATH);
const t = parseInt(readLine(), 10);
for (let tItr = 0; tItr < t; tItr++) {
const llistCount = parseInt(readLine(), 10);
let llist = new DoublyLinkedList();
for (let i = 0; i < llistCount; i++) {
const llistItem = parseInt(readLine(), 10);
llist.insertNode(llistItem);
}
let llist1 = reverse(llist.head);
printDoublyLinkedList(llist1, " ", ws)
ws.write("\n");
}
ws.end();
}
C Reverse a doubly linked list HackerRank Solution
#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 DoublyLinkedListNode DoublyLinkedListNode;
typedef struct DoublyLinkedList DoublyLinkedList;
struct DoublyLinkedListNode {
int data;
DoublyLinkedListNode* next;
DoublyLinkedListNode* prev;
};
struct DoublyLinkedList {
DoublyLinkedListNode* head;
DoublyLinkedListNode* tail;
};
DoublyLinkedListNode* create_doubly_linked_list_node(int node_data) {
DoublyLinkedListNode* node = malloc(sizeof(DoublyLinkedListNode));
node->data = node_data;
node->next = NULL;
node->prev = NULL;
return node;
}
void insert_node_into_doubly_linked_list(DoublyLinkedList** doubly_linked_list, int node_data) {
DoublyLinkedListNode* node = create_doubly_linked_list_node(node_data);
if (!(*doubly_linked_list)->head) {
(*doubly_linked_list)->head = node;
} else {
(*doubly_linked_list)->tail->next = node;
node->prev = (*doubly_linked_list)->tail;
}
(*doubly_linked_list)->tail = node;
}
void print_doubly_linked_list(DoublyLinkedListNode* node, char* sep, FILE* fptr) {
while (node) {
fprintf(fptr, "%d", node->data);
node = node->next;
if (node) {
fprintf(fptr, "%s", sep);
}
}
}
void free_doubly_linked_list(DoublyLinkedListNode* node) {
while (node) {
DoublyLinkedListNode* temp = node;
node = node->next;
free(temp);
}
}
// Complete the reverse function below.
/*
* For your reference:
*
* DoublyLinkedListNode {
* int data;
* DoublyLinkedListNode* next;
* DoublyLinkedListNode* prev;
* };
*
*/
DoublyLinkedListNode* reverse(DoublyLinkedListNode* head) {
DoublyLinkedListNode *curr = head, *next = NULL, *prev = NULL;
while (curr != NULL) {
next = curr->next;
curr->next = prev;
curr->prev = next;
prev = curr;
curr = next;
}
return prev;
}
int main()
{
FILE* fptr = fopen(getenv("OUTPUT_PATH"), "w");
char* t_endptr;
char* t_str = readline();
int t = strtol(t_str, &t_endptr, 10);
if (t_endptr == t_str || *t_endptr != '\0') { exit(EXIT_FAILURE); }
for (int t_itr = 0; t_itr < t; t_itr++) {
DoublyLinkedList* llist = malloc(sizeof(DoublyLinkedList));
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); }
insert_node_into_doubly_linked_list(&llist, llist_item);
}
DoublyLinkedListNode* llist1 = reverse(llist->head);
char *sep = " ";
print_doubly_linked_list(llist1, sep, fptr);
fprintf(fptr, "\n");
free_doubly_linked_list(llist1);
}
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; }
size_t new_length = alloc_length << 1;
data = realloc(data, new_length);
if (!data) { break; }
alloc_length = new_length;
}
if (data[data_length - 1] == '\n') {
data[data_length - 1] = '\0';
}
data = realloc(data, data_length);
return data;
}
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