Algorithm
Problem Name: Data Structures -
In this HackerRank in Data Structures -
A linked list is said to contain a cycle if any node is visited more than once while traversing the list. Given a pointer to the head of a linked list, determine if it contains a cycle. If it does, return 1. Otherwise, return 0.
Example
head refers to the list of nodes 1 -> 2 -> 3-> NULL
The numbers shown are the node numbers, not their data values. There is no cycle in this list so return 0.
head refers to the list of nodes 1 -> 2 -> 3-> 1 -> NULL
There is a cycle where node 3 points back to node 1, so return 1.
Function Description
Complete the has_cycle function in the editor below.
It has the following parameter:
- SinglyLinkedListNode pointer head: a reference to the head of the list
Returns
- int: 1 if there is a cycle or 0 if there is not
Note: If the list is empty, head will be null.
Input Format
The code stub reads from stdin and passes the appropriate argument to your function. The custom test cases format will not be described for this question due to its complexity. Expand the section for the main function and review the code if you would like to figure out how to create a custom case.
Constraints
- 0 <= list size <= 1000
Sample Input
References to each of the following linked lists are passed as arguments to your function:
Sample Output
0
1
Explanation
- The first list has no cycle, so return 0.
- The second list has a cycle, so return 1
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 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);
}
}
// Complete the has_cycle function below.
/*
* For your reference:
*
* SinglyLinkedListNode {
* int data;
* SinglyLinkedListNode* next;
* };
*
*/
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;
}
#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 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;
}
#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 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(>;
}
}
#4 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 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)
# Complete the has_cycle function below.
#
# For your reference:
#
# SinglyLinkedListNode:
# int data
# SinglyLinkedListNode next
#
#
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()