In this HackerRank Cycle Detection problem, we have given a pointer to the head of the linked list, we need to determine if the list contains a cycle or not. if true then return 1 otherwise return 0.

Hackerrank Cycle Detection problem solution


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 insert_node(self, node_data):
        node = SinglyLinkedListNode(node_data)

        if not self.head:
            self.head = node
        else:
            self.tail.next = node


        self.tail = node

def print_singly_linked_list(node, sep, fptr):
    while node:
        fptr.write(str(node.data))

        node = node.next

        if node:
            fptr.write(sep)


def has_cycle(head):
    visited = set()
    f = head
    while f:
        i = id(f)
        if i in visited:
            return 1
        visited.add(i)
        f = f.next
    return 0

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

    tests = int(input())

    for tests_itr in range(tests):
        index = int(input())

        llist_count = int(input())

        llist = SinglyLinkedList()

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

        extra = SinglyLinkedListNode(-1);
        temp = llist.head;

        for i in range(llist_count):
            if i == index:
                extra = temp

            if i != llist_count-1:
                temp = temp.next

        temp.next = extra

        result = has_cycle(llist.head)

        fptr.write(str(int(result)) + '\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 void insertNode(int nodeData) {
            SinglyLinkedListNode node = new SinglyLinkedListNode(nodeData);

            if (this.head == null) {
                this.head = node;
            } else {
                this.tail.next = node;
            }

            this.tail = node;
        }
    }

    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 boolean hasCycle(SinglyLinkedListNode head) {

    Set<SinglyLinkedListNode> set=new HashSet<>();
    while(head!=null){
    if(set.contains(head.next))
    return true;
    set.add(head.next);
    head=head.next;
    }
    return false;
}

    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 tests = scanner.nextInt();
        scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

        for (int testsItr = 0; testsItr < tests; testsItr++) {
            int index = scanner.nextInt();
            scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

            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])?");

                llist.insertNode(llistItem);
            }
          
            SinglyLinkedListNode extra = new SinglyLinkedListNode(-1);
            SinglyLinkedListNode temp = llist.head;

            for (int i = 0; i < llistCount; i++) {
                if (i == index) {
                    extra = temp;
                }

                if (i != llistCount-1) {
                    temp = temp.next;
                }
            }
      
          temp.next = extra;

            boolean result = hasCycle(llist.head);

            bufferedWriter.write(String.valueOf(result ? 1 : 0));
            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 insert_node(int node_data) {
            SinglyLinkedListNode* node = new SinglyLinkedListNode(node_data);

            if (!this->head) {
                this->head = node;
            } else {
                this->tail->next = node;
            }

            this->tail = node;
        }
};

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);
    }
}


bool has_cycle(SinglyLinkedListNode* head) {
SinglyLinkedListNode* cur1 = head;
    SinglyLinkedListNode* cur2 = head;
    int result = 0;
    while (cur1 && cur2)
    {
        cur1 = cur1->next;
        cur2 = cur2->next;
        if (cur2)
        {
            cur2 = cur2->next;
        }
        
        if (cur1 == cur2)
        {
            result = 1;
            break;
        }
    }
    return result;

}

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

    int tests;
    cin >> tests;
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    for (int tests_itr = 0; tests_itr < tests; tests_itr++) {
        int index;
        cin >> index;
        cin.ignore(numeric_limits<streamsize>::max(), '\n');

        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');

            llist->insert_node(llist_item);
        }
      
        SinglyLinkedListNode* extra = new SinglyLinkedListNode(-1);
        SinglyLinkedListNode* temp = llist->head;
      
        for (int i = 0; i < llist_count; i++) {
            if (i == index) {
                extra = temp;
            }
            
            if (i != llist_count-1) {
                temp = temp->next;
            }
        }
      
        temp->next = extra;

        bool result = has_cycle(llist->head);

        fout << result << "\n";
    }

    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 insert_node_into_singly_linked_list(SinglyLinkedList** singly_linked_list, int node_data) {
    SinglyLinkedListNode* node = create_singly_linked_list_node(node_data);

    if (!(*singly_linked_list)->head) {
        (*singly_linked_list)->head = node;
    } else {
        (*singly_linked_list)->tail->next = node;
    }

    (*singly_linked_list)->tail = 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);
    }
}


bool has_cycle(SinglyLinkedListNode* head) {

    SinglyLinkedListNode * nodePtr = head;
    int i;
    
    for ( i=0; i < 1000; i++ )
    {
        if ( !nodePtr )
            break;
        nodePtr = nodePtr->next;
    }
    
    if ( i >= 1000 )
        return true;
    else
        return false;
}

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

    char* tests_endptr;
    char* tests_str = readline();
    int tests = strtol(tests_str, &tests_endptr, 10);

    if (tests_endptr == tests_str || *tests_endptr != '\0') { exit(EXIT_FAILURE); }

    for (int tests_itr = 0; tests_itr < tests; tests_itr++) {
        char* index_endptr;
        char* index_str = readline();
        int index = strtol(index_str, &index_endptr, 10);

        if (index_endptr == index_str || *index_endptr != '\0') { exit(EXIT_FAILURE); }

        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); }

            insert_node_into_singly_linked_list(&llist, llist_item);
        }
      
        SinglyLinkedListNode* extra = create_singly_linked_list_node(-1);
        SinglyLinkedListNode* temp = llist->head;
      
        for (int i = 0; i < llist_count; i++) {
            if (i == index) {
                extra = temp;
            }
            
            if (i != llist_count-1) {
                temp = temp->next;
            }
        }
      
        temp->next = extra;

        bool result = has_cycle(llist->head);

        fprintf(fptr, "%d\n", result);
    }

    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;
}