In this HackerRank Find Merge Point of Two Lists Interview preparation kit problem, You have Given pointers to the head nodes of 2 linked lists that merge together at some point, find the node where the two lists merge.

HackerRank Find Merge Point of Two Lists interview preparation kit 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)

# Complete the findMergeNode function below.

#
# For your reference:
#
# SinglyLinkedListNode:
#     int data
#     SinglyLinkedListNode next
#
#
def findMergeNode(headA, headB):
    
    while headA:
        node = headB
        while node:
            if headA == node:
                return headA.data
            node = node.next
        headA = headA.next

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

    tests = int(input())

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

        llist1_count = int(input())

        llist1 = SinglyLinkedList()

        for _ in range(llist1_count):
            llist1_item = int(input())
            llist1.insert_node(llist1_item)
            
        llist2_count = int(input())

        llist2 = SinglyLinkedList()

        for _ in range(llist2_count):
            llist2_item = int(input())
            llist2.insert_node(llist2_item)
            
        ptr1 = llist1.head;
        ptr2 = llist2.head;

        for i in range(llist1_count):
            if i < index:
                ptr1 = ptr1.next
                
        for i in range(llist2_count):
            if i != llist2_count-1:
                ptr2 = ptr2.next

        ptr2.next = ptr1

        result = findMergeNode(llist1.head, llist2.head)

        fptr.write(str(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);
            }
        }
    }

    // Complete the findMergeNode function below.

    /*
     * For your reference:
     *
     * SinglyLinkedListNode {
     *     int data;
     *     SinglyLinkedListNode next;
     * }
     *
     */
    static int findMergeNode(SinglyLinkedListNode head1, SinglyLinkedListNode head2) {

SinglyLinkedListNode temp1=head1;
    SinglyLinkedListNode temp2=head2;
    List<SinglyLinkedListNode>list=new ArrayList<SinglyLinkedListNode>();
    while(temp1!=null){
        list.add(temp1);
        temp1=temp1.next;            
    }
    while(temp2!=null){
        if(list.contains(temp2)){
            break;
        }
        temp2=temp2.next;
    }
    return temp2.data;

    }

    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 llist1 = new SinglyLinkedList();

            int llist1Count = scanner.nextInt();
            scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

            for (int i = 0; i < llist1Count; i++) {
                int llist1Item = scanner.nextInt();
                scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

                llist1.insertNode(llist1Item);
            }
          
            SinglyLinkedList llist2 = new SinglyLinkedList();

            int llist2Count = scanner.nextInt();
            scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

            for (int i = 0; i < llist2Count; i++) {
                int llist2Item = scanner.nextInt();
                scanner.skip("(\r\n|[\n\r\u2028\u2029\u0085])?");

                llist2.insertNode(llist2Item);
            }
          
            SinglyLinkedListNode ptr1 = llist1.head;
            SinglyLinkedListNode ptr2 = llist2.head;

            for (int i = 0; i < llist1Count; i++) {
                if (i < index) {
                    ptr1 = ptr1.next;
                }
            }

            for (int i = 0; i < llist2Count; i++) {
                if (i != llist2Count-1) {
                    ptr2 = ptr2.next;
                }
            }

            ptr2.next = ptr1;

            int result = findMergeNode(llist1.head, llist2.head);

            bufferedWriter.write(String.valueOf(result));
            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);
    }
}

// Complete the findMergeNode function below.

/*
 * For your reference:
 *
 * SinglyLinkedListNode {
 *     int data;
 *     SinglyLinkedListNode* next;
 * };
 *
 */
int findMergeNode(SinglyLinkedListNode* headA, SinglyLinkedListNode* headB) {
    while(headA){
        SinglyLinkedListNode *tmp = headA->next;
        headA->next = NULL;
        headA = tmp;
    }
    
    while(headB){
        if(headB->next == NULL){
            return headB->data;
        }
        headB = headB->next;
    }
    return 0;
}

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* llist1 = new SinglyLinkedList();

        int llist1_count;
        cin >> llist1_count;
        cin.ignore(numeric_limits<streamsize>::max(), '\n');

        for (int i = 0; i < llist1_count; i++) {
            int llist1_item;
            cin >> llist1_item;
            cin.ignore(numeric_limits<streamsize>::max(), '\n');

            llist1->insert_node(llist1_item);
        }
      
        SinglyLinkedList* llist2 = new SinglyLinkedList();

        int llist2_count;
        cin >> llist2_count;
        cin.ignore(numeric_limits<streamsize>::max(), '\n');

        for (int i = 0; i < llist2_count; i++) {
            int llist2_item;
            cin >> llist2_item;
            cin.ignore(numeric_limits<streamsize>::max(), '\n');

            llist2->insert_node(llist2_item);
        }
      
        SinglyLinkedListNode* ptr1 = llist1->head;
        SinglyLinkedListNode* ptr2 = llist2->head;
      
        for (int i = 0; i < llist1_count; i++) {
            if (i < index) {
                ptr1 = ptr1->next;
            }
        }
      
        for (int i = 0; i < llist2_count; i++) {
            if (i != llist2_count-1) {
                ptr2 = ptr2->next;
            }
        }
      
        ptr2->next = ptr1;

        int result = findMergeNode(llist1->head, llist2->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);
    }
}

// Complete the findMergeNode function below.

/*
 * For your reference:
 *
 * SinglyLinkedListNode {
 *     int data;
 *     SinglyLinkedListNode* next;
 * };
 *
 */
int findMergeNode(SinglyLinkedListNode* headA, SinglyLinkedListNode* headB) {
    while(headA){
        SinglyLinkedListNode *tmp = headA->next;
        headA->next = NULL;
        headA = tmp;
    }
    
    while(headB){
        if(headB->next == NULL){
            return headB->data;
        }
        headB = headB->next;
    }
    return 0;
}

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* llist1 = malloc(sizeof(SinglyLinkedList));
        llist1->head = NULL;
        llist1->tail = NULL;

        char* llist1_count_endptr;
        char* llist1_count_str = readline();
        int llist1_count = strtol(llist1_count_str, &llist1_count_endptr, 10);

        if (llist1_count_endptr == llist1_count_str || *llist1_count_endptr != '\0') { exit(EXIT_FAILURE); }

        for (int i = 0; i < llist1_count; i++) {
            char* llist1_item_endptr;
            char* llist1_item_str = readline();
            int llist1_item = strtol(llist1_item_str, &llist1_item_endptr, 10);

            if (llist1_item_endptr == llist1_item_str || *llist1_item_endptr != '\0') { exit(EXIT_FAILURE); }

            insert_node_into_singly_linked_list(&llist1, llist1_item);
        }
      
        SinglyLinkedList* llist2 = malloc(sizeof(SinglyLinkedList));
        llist2->head = NULL;
        llist2->tail = NULL;

        char* llist2_count_endptr;
        char* llist2_count_str = readline();
        int llist2_count = strtol(llist2_count_str, &llist2_count_endptr, 10);

        if (llist2_count_endptr == llist2_count_str || *llist2_count_endptr != '\0') { exit(EXIT_FAILURE); }

        for (int i = 0; i < llist2_count; i++) {
            char* llist2_item_endptr;
            char* llist2_item_str = readline();
            int llist2_item = strtol(llist2_item_str, &llist2_item_endptr, 10);

            if (llist2_item_endptr == llist2_item_str || *llist2_item_endptr != '\0') { exit(EXIT_FAILURE); }

            insert_node_into_singly_linked_list(&llist2, llist2_item);
        }
      
        SinglyLinkedListNode* ptr1 = llist1->head;
        SinglyLinkedListNode* ptr2 = llist2->head;
      
        for (int i = 0; i < llist1_count; i++) {
            if (i < index) {
                ptr1 = ptr1->next;
            }
        }
      
        for (int i = 0; i < llist2_count; i++) {
            if (i != llist2_count-1) {
                ptr2 = ptr2->next;
            }
        }
      
        ptr2->next = ptr1;

        int result = findMergeNode(llist1->head, llist2->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;
}


Problem solution in 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', _ => {
    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;
    }

    insertNode(nodeData) {
        const node = new SinglyLinkedListNode(nodeData);

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

        this.tail = node;
    }
};

function printSinglyLinkedList(node, sep, ws) {
    while (node != null) {
        ws.write(String(node.data));

        node = node.next;

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

/*
    Find merge point of two linked lists
    Note that the head may be 'null' for the empty list.
    Node is defined as
    var Node = function(data) {
        this.data = data;
        this.next = null;
    }
*/

// This is a "method-only" submission.
// You only need to complete this method.

function findMergeNode(a, b) {
    let arr = [];
    
    while (a || b) {
        if (a && arr.find(n => n === a)) return a.data;
        else if(a) {
            arr.push(a)
            a = a.next;
        }
        if (b && arr.find(n => n === b)) return b.data;
        else if (b) {
            arr.push(b);
            b = b.next;
        }
    }
    
    return 0;
}

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

    const tests = parseInt(readLine(), 10);

    for (let testsItr = 0; testsItr < tests; testsItr++) {
        const index = parseInt(readLine(), 10);

        const llist1Count = parseInt(readLine(), 10);

        let llist1 = new SinglyLinkedList();

        for (let i = 0; i < llist1Count; i++) {
            const llist1Item = parseInt(readLine(), 10);
            llist1.insertNode(llist1Item);
        }
      
        const llist2Count = parseInt(readLine(), 10);

        let llist2 = new SinglyLinkedList();

        for (let i = 0; i < llist2Count; i++) {
            const llist2Item = parseInt(readLine(), 10);
            llist2.insertNode(llist2Item);
        }
      
        let ptr1 = llist1.head;
        let ptr2 = llist2.head;

        for (let i = 0; i < llist1Count; i++) {
          if (i < index) {
            ptr1 = ptr1.next;
          }
        }

        for (let i = 0; i < llist2Count; i++) {
          if (i != llist2Count-1) {
            ptr2 = ptr2.next;
          }
        }

        ptr2.next = ptr1;

        let result = findMergeNode(llist1.head, llist2.head);

        ws.write(result + "\n");
    }

    ws.end();
}