Algorithm
Problem Name: Data Structures -
In this HackerRank in Data Structures -
Given pointers to the head nodes of 2 linked lists that merge together at some point, find the node where the two lists merge. The merge point is where both lists point to the same node, i.e. they reference the same memory location. It is guaranteed that the two head nodes will be different, and neither will be NULL. If the lists share a common node, return that node's data value.
Note: After the merge point, both lists will share the same node pointers.
Example
In the diagram below, the two lists converge at Node x:
[List #1] a--->b--->c
\
x--->y--->z--->NULL
/
[List #2] p--->q
Function Description
Complete the findMergeNode function in the editor below.
findMergeNode has the following parameters:
- SinglyLinkedListNode pointer head1: a reference to the head of the first list
- SinglyLinkedListNode pointer head2: a reference to the head of the second list
Returns
- int: the data value of the node where the lists merge
Input Format
Do not read any input from stdin/console.
The first line contains an integer t, the number of test cases. Each of the test cases is in the following format:
The first line contains an integer, index, the node number where the merge will occur.
The next line contains an integer, list1Count lines contains a data value for a node. The next line contains an integer, list2Count that is the number of nodes in the second list.
Each of the following list1Count lines contains a data value for a node.
Constraints
The lists will merge.
head1,head2 not= null
head1 not= head2
Sample Input
The diagrams below are graphical representations of the lists that input nodes head1 and head2 are connected to.
Test Case 0
1
\
2--->3--->NULL
/
1
Test Case 1
1--->2
\
3--->Null
/
1
Sample Output
2
3
Explanation
Test Case 0: As demonstrated in the diagram above, the merge node's data field contains the integer 2.
Test Case 1: As demonstrated in the diagram above, the merge node's data field contains the integer 3.
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 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;
}
#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);
}
}
// 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;
}
#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);
}
}
}
// 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();
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(>;
}
}
#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', _ => {
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(>;
}
#5 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 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()