Given a linked list, and a number, check if their exist two numbers whose sum is equal to given number. If there exist two numbers, print them. If there are multiple answer, print any of them.
Examples:
Input : 1 -> 2 -> 3 -> 4 -> 5 -> NULL
sum = 3
Output : Pair is (1, 2)
Input : 10 -> 12 -> 31 -> 42 -> 53 -> NULL
sum = 15
Output : NO PAIR EXIST
Method(Brute force): Iteratively check if their exist any pair or not
Implementation:
C++
// CPP code to find the pair with given sum
#include <bits/stdc++.h>
using namespace std;
/* Link list node */
struct Node {
int data;
struct Node* next;
};
/* Given a reference (pointer to pointer)
to the head of a list and an int,
push a new node on the front
of the list. */
void push(struct Node** head_ref, int new_data)
{
/* allocate node */
struct Node* new_node =
(struct Node*)malloc(sizeof(struct Node));
/* put in the data */
new_node->data = new_data;
/* link the old list of the new node */
new_node->next = (*head_ref);
/* move the head to point to the new node */
(*head_ref) = new_node;
}
/* Takes head pointer of the linked list and sum*/
int check_pair_sum(struct Node* head, int sum)
{
struct Node* p = head, *q;
while (p != NULL) {
q = p->next;
while (q != NULL) {
// check if both sum is equal to
// given sum
if ((p->data) + (q->data) == sum) {
cout << p->data << " " << q->data;
return true;
}
q = q->next;
}
p = p->next;
}
return 0;
}
/* Driver program to test above function */
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
/* Use push() to construct linked list*/
push(&head, 1);
push(&head, 4);
push(&head, 1);
push(&head, 12);
push(&head, 1);
push(&head, 18);
push(&head, 47);
push(&head, 16);
push(&head, 12);
push(&head, 14);
/* function to print the result*/
bool res = check_pair_sum(head, 26);
if (res == false)
cout << "NO PAIR EXIST";
return 0;
}
// Java code to find the pair with given sum
import java.util.*;
class GFG {
/* Link list node */
static class Node {
int data;
Node next;
};
static Node head;
/* Given a reference (pointer to pointer)
to the head of a list and an int,
push a new node on the front
of the list. */
// Inserting node at the beginning
static Node push(Node head_ref, int new_data)
{
/* allocate node */
Node new_node = new Node();
/* put in the data */
new_node.data = new_data;
/* link the old list to the new node */
new_node.next = head_ref;
/* move the head to point to the new node */
head_ref = new_node;
return head = head_ref;
}
/* Takes head pointer of the linked list and sum*/
static boolean check_pair_sum(Node head, int sum)
{
Node p = head, q;
while (p != null)
{
q = p.next;
while (q != null)
{
// check if both sum is equal to
// given sum
if ((p.data) + (q.data) == sum)
{
System.out.print(p.data + " " + q.data);
return true;
}
q = q.next;
}
p = p.next;
}
return false;
}
// Driver Code
public static void main(String[] args)
{
/* Start with the empty list */
head = null;
/* Use push() to construct linked list*/
push(head, 1);
push(head, 4);
push(head, 1);
push(head, 12);
push(head, 1);
push(head, 18);
push(head, 47);
push(head, 16);
push(head, 12);
push(head, 14);
/* function to print the result*/
boolean res = check_pair_sum(head, 26);
if (res == false)
System.out.print("NO PAIR EXIST");
}
}
// This code is contributed by 29AjayKumar
# Python3 program for finding the pair with given sum
import math
import sys
# Link list node #
class Node:
def __init__(self, data):
self.data = data
self.next = None
# Given a reference (pointer to pointer) to the head
# of a list and an int, push a new node on the front
# of the list.
def push(head, data):
if head == None:
return Node(data)
# allocate node
temp = Node(data)
# link the old list of the new node
temp.next = head
# move the head to point to the new node
head = temp
return head
# Takes head pointer of the linked list and sum
def check_pair_sum(head, _sum_):
p = head
q = None
while(p):
q = p.next
while(q):
if p.data+q.data == _sum_:
print("{} {}".format(p.data, q.data))
return True
q = q.next
p = p.next
return False
# Driver program to test above function
if __name__ == '__main__':
# Start with the empty list
head = None
# Use push() to construct linked list
head = push(head, 1)
head = push(head, 4)
head = push(head, 1)
head = push(head, 12)
head = push(head, 1)
head = push(head, 18)
head = push(head, 47)
head = push(head, 16)
head = push(head, 12)
head = push(head, 14)
# function to print the result
res = check_pair_sum(head, 26)
if (res == False):
print("NO PAIR EXIST")
# This code is contributed by Vikash Kumar 37
// C# code to find the pair with given sum
using System;
class GFG {
/* Link list node */
public class Node {
public int data;
public Node next;
};
static Node head;
/* Given a reference (pointer to pointer)
to the head of a list and an int,
push a new node on the front
of the list. */
// Inserting node at the beginning
static Node push(Node head_ref, int new_data)
{
/* allocate node */
Node new_node = new Node();
/* put in the data */
new_node.data = new_data;
/* link the old list to the new node */
new_node.next = head_ref;
/* move the head to point to the new node */
head_ref = new_node;
return head = head_ref;
}
/* Takes head pointer of the linked list and sum*/
static Boolean check_pair_sum(Node head, int sum)
{
Node p = head, q;
while (p != null)
{
q = p.next;
while (q != null)
{
// check if both sum is equal to
// given sum
if ((p.data) + (q.data) == sum)
{
Console.Write(p.data + " " + q.data);
return true;
}
q = q.next;
}
p = p.next;
}
return false;
}
// Driver Code
public static void Main(String[] args)
{
/* Start with the empty list */
head = null;
/* Use push() to construct linked list*/
push(head, 1);
push(head, 4);
push(head, 1);
push(head, 12);
push(head, 1);
push(head, 18);
push(head, 47);
push(head, 16);
push(head, 12);
push(head, 14);
/* function to print the result*/
Boolean res = check_pair_sum(head, 26);
if (res == false)
Console.Write("NO PAIR EXIST");
}
}
// This code is contributed by Rajput-Ji
<script>
// JavaScript code to find the pair with given sum
/* Link list node */
class Node {
constructor()
{
this.data = 0;
this.next = null;
}
};
var head = null;
/* Given a reference (pointer to pointer)
to the head of a list and an int,
push a new node on the front
of the list. */
// Inserting node at the beginning
function push(head_ref, new_data)
{
/* allocate node */
var new_node = new Node();
/* put in the data */
new_node.data = new_data;
/* link the old list to the new node */
new_node.next = head_ref;
/* move the head to point to the new node */
head_ref = new_node;
return head = head_ref;
}
/* Takes head pointer of the linked list and sum*/
function check_pair_sum(head, sum)
{
var p = head, q;
while (p != null)
{
q = p.next;
while (q != null)
{
// check if both sum is equal to
// given sum
if ((p.data) + (q.data) == sum)
{
document.write(p.data + " " + q.data);
return true;
}
q = q.next;
}
p = p.next;
}
return false;
}
// Driver Code
/* Start with the empty list */
head = null;
/* Use push() to construct linked list*/
push(head, 1);
push(head, 4);
push(head, 1);
push(head, 12);
push(head, 1);
push(head, 18);
push(head, 47);
push(head, 16);
push(head, 12);
push(head, 14);
/* function to print the result*/
var res = check_pair_sum(head, 26);
if (res == false)
document.write("NO PAIR EXIST");
</script>
Time complexity: O(n*n)
Auxiliary Space: O(1)
Method 2 (using hashing):
- Take a hashtable and mark all element with zero
- Iteratively mark all the element as 1 in hashtable which are present in linked list
- Iteratively find sum-current element of linked list is present in hashtable or not
Implementation:
C++
// CPP program to for finding the pair with given sum
#include <bits/stdc++.h>
#define MAX 100000
using namespace std;
/* Link list node */
struct Node {
int data;
struct Node* next;
};
/* Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. */
void push(struct Node** head_ref, int new_data)
{
/* allocate node */
struct Node* new_node =
(struct Node*)malloc(sizeof(struct Node));
/* put in the data */
new_node->data = new_data;
/* link the old list of the new node */
new_node->next = (*head_ref);
/* move the head to point to the new node */
(*head_ref) = new_node;
}
/* Takes head pointer of the linked list and sum*/
bool check_pair_sum(struct Node* head, int sum)
{
unordered_set<int> s;
struct Node* p = head;
while (p != NULL) {
int curr = p->data;
if (s.find(sum - curr) != s.end())
{
cout << curr << " " << sum - curr;
return true;
}
s.insert(p->data);
p = p->next;
}
return false;
}
/* Driver program to test above function*/
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
/* Use push() to construct linked list */
push(&head, 1);
push(&head, 4);
push(&head, 1);
push(&head, 12);
push(&head, 1);
push(&head, 18);
push(&head, 47);
push(&head, 16);
push(&head, 12);
push(&head, 14);
/* function to print the result*/
bool res = check_pair_sum(head, 26);
if (res == false)
cout << "NO PAIR EXIST";
return 0;
}
// Java program for finding
// the pair with given sum
import java.util.*;
class GFG {
static int MAX = 100000;
/* Link list node */
static class Node {
int data;
Node next;
};
static Node head;
/* Given a reference (pointer to pointer)
to the head of a list and an int,
push a new node on the front of the list. */
static void push(Node head_ref, int new_data)
{
/* allocate node */
Node new_node = new Node();
/* put in the data */
new_node.data = new_data;
/* link the old list of the new node */
new_node.next = head_ref;
/* move the head to point to the new node */
head_ref = new_node;
head = head_ref;
}
/* Takes head pointer of the linked list and sum*/
static boolean check_pair_sum(Node head, int sum)
{
HashSet<Integer> s = new HashSet<Integer>();
Node p = head;
while (p != null)
{
int curr = p.data;
if (s.contains(sum - curr))
{
System.out.print(curr + " " + (sum - curr));
return true;
}
s.add(p.data);
p = p.next;
}
return false;
}
// Driver Code
public static void main(String[] args)
{
/* Start with the empty list */
head = null;
/* Use push() to construct linked list */
push(head, 1);
push(head, 4);
push(head, 1);
push(head, 12);
push(head, 1);
push(head, 18);
push(head, 47);
push(head, 16);
push(head, 12);
push(head, 14);
/* function to print the result*/
boolean res = check_pair_sum(head, 26);
if (res == false)
System.out.print("NO PAIR EXIST");
}
}
// This code is contributed by PrinciRaj1992
# Python3 program to for finding the pair with given sum
MAX = 100000
''' Link list node '''
class Node:
def __init__(self, data):
self.data = data
self.next = None
''' Given a reference (pointer to pointer) to the head
of a list and an int, push a new node on the front
of the list. '''
def push(head_ref, new_data):
''' allocate node '''
new_node = Node(new_data)
''' put in the data '''
new_node.data = new_data
''' link the old list of the new node '''
new_node.next = (head_ref)
''' move the head to point to the new node '''
(head_ref) = new_node
return head_ref
''' Takes head pointer of the linked list and sum'''
def check_pair_sum(head, sum):
s = set()
p = head
while (p != None):
curr = p.data
if((sum - curr) in s):
print(curr, end=' ')
print(sum-curr, end='')
return True
s.add(p.data)
p = p.next
return False
''' Driver program to test above function'''
if __name__ == '__main__':
''' Start with the empty list '''
head = None
''' Use push() to construct linked list '''
head = push(head, 1)
head = push(head, 4)
head = push(head, 1)
head = push(head, 12)
head = push(head, 1)
head = push(head, 18)
head = push(head, 47)
head = push(head, 16)
head = push(head, 12)
head = push(head, 14)
''' function to print the result'''
res = check_pair_sum(head, 26)
if (res == False):
print("NO PAIR EXIST")
# This code is contributed by rutvik_56
// C# program for finding
// the pair with given sum
using System;
using System.Collections.Generic;
class GFG {
static int MAX = 100000;
/* Link list node */
public class Node {
public int data;
public Node next;
};
static Node head;
/* Given a reference (pointer to pointer)
to the head of a list and an int,
push a new node on the front of the list. */
static void push(Node head_ref, int new_data)
{
/* allocate node */
Node new_node = new Node();
/* put in the data */
new_node.data = new_data;
/* link the old list of the new node */
new_node.next = head_ref;
/* move the head to point to the new node */
head_ref = new_node;
head = head_ref;
}
/* Takes head pointer of the linked list and sum*/
static Boolean check_pair_sum(Node head, int sum)
{
HashSet<int> s = new HashSet<int>();
Node p = head;
while (p != null)
{
int curr = p.data;
if (s.Contains(sum - curr))
{
Console.Write(curr + " " + (sum - curr));
return true;
}
s.Add(p.data);
p = p.next;
}
return false;
}
// Driver Code
public static void Main(String[] args)
{
/* Start with the empty list */
head = null;
/* Use push() to construct linked list */
push(head, 1);
push(head, 4);
push(head, 1);
push(head, 12);
push(head, 1);
push(head, 18);
push(head, 47);
push(head, 16);
push(head, 12);
push(head, 14);
/* function to print the result*/
Boolean res = check_pair_sum(head, 26);
if (res == false)
Console.Write("NO PAIR EXIST");
}
}
// This code is contributed by Princi Singh
<script>
// JavaScript program for finding
// the pair with given sum
const MAX = 100000;
/* Link list node */
class Node {
constructor() {
this.data = 0;
this.next = null;
}
}
var head = null;
/* Given a reference (pointer to pointer)
to the head of a list and an int,
push a new node on the front of the list. */
function push(head_ref, new_data) {
/* allocate node */
var new_node = new Node();
/* put in the data */
new_node.data = new_data;
/* link the old list of the new node */
new_node.next = head_ref;
/* move the head to point to the new node */
head_ref = new_node;
head = head_ref;
}
/* Takes head pointer of the linked list and sum*/
function check_pair_sum(head, sum) {
var s = new Set();
var p = head;
while (p != null)
{
var curr = p.data;
if (s.has(sum - curr))
{
document.write(curr + " " + (sum - curr));
return true;
}
s.add(p.data);
p = p.next;
}
return false;
}
// Driver Code
/* Start with the empty list */
head = null;
/* Use push() to construct linked list */
push(head, 1);
push(head, 4);
push(head, 1);
push(head, 12);
push(head, 1);
push(head, 18);
push(head, 47);
push(head, 16);
push(head, 12);
push(head, 14);
/* function to print the result*/
var res = check_pair_sum(head, 26);
if (res == false) document.write("NO PAIR EXIST");
// This code is contributed by rdtank.
</script>
Time complexity: O(n)
Auxiliary Space: O(n)
Method 3 (using recursion):
Traverse through each node and find if element Sum-(node->data) is available in remaining linked list or not. If not, current node will not be a part of solution. For each node the list is traversed a single time. So, the overall time complexity is quadratic, but no additional space is required for this solution. Although we are using additional stack space for recursion.
Implementation:
C++
// C++ implementation of the above approach
#include<bits/stdc++.h>
using namespace std;
/* Link list node */
struct Node {
int data;
struct Node* next;
};
void push(struct Node** head_ref, int new_data)
{
struct Node* new_node = new Node();
new_node->data = new_data;
new_node->next = (*head_ref);
(*head_ref) = new_node;
}
bool findElement(struct Node* head, int element)
{
if (head == NULL)
{
return false;
}
else if (head->data == element)
{
return true;
}
return findElement(head->next, element);
}
bool check_pair_sum(struct Node* head, int sum)
{
bool found = false;
while (head != NULL)
{
found = findElement(head, sum - head->data);
if (found == true)
{
cout<<head->data<<" and "<<(sum-head->data);
return found;
}
head = head->next;
}
return found;
}
// Driver Code
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
/* Use push() to construct linked list*/
push(&head, 1);
push(&head, 4);
push(&head, 1);
push(&head, 12);
push(&head, 1);
push(&head, 18);
push(&head, 47);
push(&head, 16);
push(&head, 12);
push(&head, 14);
push(&head, 0);
/* Function to print the result*/
bool res = check_pair_sum(head, 26);
if (res == false)
cout<<"No pair found";
return 0;
}
// This code is contributed by Yash Agarwal(yashagarwal2852002)
// C++ implementation of the above approach
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
/* Link list node */
struct Node {
int data;
struct Node* next;
};
void push(struct Node** head_ref, int new_data)
{
struct Node* new_node
= (struct Node*)malloc(sizeof(struct Node));
new_node->data = new_data;
new_node->next = (*head_ref);
(*head_ref) = new_node;
}
bool findElement(struct Node* head, int element)
{
if (head == NULL)
{
return false;
}
else if (head->data == element)
{
return true;
}
return findElement(head->next, element);
}
bool check_pair_sum(struct Node* head, int sum)
{
bool found = false;
while (head != NULL)
{
found = findElement(head, sum - head->data);
if (found == true)
{
printf("%d and %d \n", head->data,
sum - head->data);
return found;
}
head = head->next;
}
return found;
}
// Driver Code
int main()
{
/* Start with the empty list */
struct Node* head = NULL;
/* Use push() to construct linked list*/
push(&head, 1);
push(&head, 4);
push(&head, 1);
push(&head, 12);
push(&head, 1);
push(&head, 18);
push(&head, 47);
push(&head, 16);
push(&head, 12);
push(&head, 14);
push(&head, 0);
/* Function to print the result*/
bool res = check_pair_sum(head, 26);
if (res == false)
printf("No pair found");
return 0;
}
// Java implementation of the above approach
// Node class
class Node {
int data;
Node next;
Node(int data)
{
this.data = data;
this.next = null;
}
}
// Function to add new node at the beginning
class LinkedList {
static Node push(Node head_ref, int new_data)
{
Node new_node = new Node(new_data);
new_node.next = head_ref;
head_ref = new_node;
return head_ref;
}
}
// Function to find an element in the linked list
class Search {
static boolean findElement(Node head, int element)
{
if (head == null) {
return false;
}
else if (head.data == element) {
return true;
}
return findElement(head.next, element);
}
}
// Function to check if there exists a pair with given sum
class PairSum {
static boolean check_pair_sum(Node head, int sum)
{
boolean found = false;
while (head != null) {
found
= Search.findElement(head, sum - head.data);
if (found == true) {
System.out.println(head.data + " and "
+ (sum - head.data));
return found;
}
head = head.next;
}
return found;
}
}
// Driver code
class Main {
public static void main(String[] args)
{
// Start with the empty list
Node head = null;
// Use push() to construct linked list
head = LinkedList.push(head, 1);
head = LinkedList.push(head, 4);
head = LinkedList.push(head, 1);
head = LinkedList.push(head, 12);
head = LinkedList.push(head, 1);
head = LinkedList.push(head, 18);
head = LinkedList.push(head, 47);
head = LinkedList.push(head, 16);
head = LinkedList.push(head, 12);
head = LinkedList.push(head, 14);
head = LinkedList.push(head, 0);
// Function to print the result
boolean res = PairSum.check_pair_sum(head, 26);
if (res == false)
System.out.println("No pair found");
}
}
// This code is contributed by divyansh2212
# Python implementation of the above approach
# Node class
class Node:
def __init__(self, data):
self.data = data
self.next = None
# Function to add new node at the beginning
def push(head_ref, new_data):
new_node = Node(new_data)
new_node.next = head_ref
head_ref = new_node
return head_ref
# Function to find an element in the linked list
def findElement(head, element):
if (head == None):
return False
elif (head.data == element):
return True
return findElement(head.next, element)
# Function to check if there exists a pair with given sum
def check_pair_sum(head, sum):
found = False
while (head != None):
found = findElement(head, sum - head.data)
if (found == True):
print(head.data, "and", (sum - head.data))
return found
head = head.next
return found
# Driver code
if __name__ == '__main__':
# Start with the empty list
head = None
# Use push() to construct linked list
head = push(head, 1)
head = push(head, 4)
head = push(head, 1)
head = push(head, 12)
head = push(head, 1)
head = push(head, 18)
head = push(head, 47)
head = push(head, 16)
head = push(head, 12)
head = push(head, 14)
head = push(head, 0)
# Function to print the result
res = check_pair_sum(head, 26)
if (res == False):
print("No pair found")
using System;
public class LinkedList
{
/* Link list node */
public class Node
{
public int data;
public Node next;
}
public static void Push(ref Node head_ref, int new_data)
{
Node new_node = new Node();
new_node.data = new_data;
new_node.next = head_ref;
head_ref = new_node;
}
public static bool FindElement(Node head, int element)
{
if (head == null)
{
return false;
}
else if (head.data == element)
{
return true;
}
return FindElement(head.next, element);
}
public static bool CheckPairSum(Node head, int sum)
{
bool found = false;
while (head != null)
{
found = FindElement(head, sum - head.data);
if (found == true)
{
Console.WriteLine(head.data + " and " + (sum - head.data));
return found;
}
head = head.next;
}
return found;
}
// Driver Code
public static void Main()
{
/* Start with the empty list */
Node head = null;
/* Use Push() to construct linked list*/
Push(ref head, 1);
Push(ref head, 4);
Push(ref head, 1);
Push(ref head, 12);
Push(ref head, 1);
Push(ref head, 18);
Push(ref head, 47);
Push(ref head, 16);
Push(ref head, 12);
Push(ref head, 14);
Push(ref head, 0);
/* Function to print the result*/
bool res = CheckPairSum(head, 26);
if (res == false)
Console.WriteLine("No pair found");
}
}
Javascript// Javascript program of the above approach
// link list node
class Node{
constructor(data){
this.data = data;
this.next = null;
}
}
function push(head_ref, new_data){
let new_node = new Node(new_data);
new_node.next = head_ref;
// head_ref = new_node;
return new_node;
}
function findElement(head, element){
if(head == null) return false;
else if(head.data == element) return true;
return findElement(head.next, element);
}
function check_pair_sum(head, sum){
let found = false;
while(head != null){
found = findElement(head, sum - head.data);
if(found == true){
document.write(head.data + " and " + (sum-head.data));
return found;
}
head = head.next;
}
return found;
}
// driver code
// start with empty list
let head = null;
head = push(head, 1);
head = push(head, 4);
head = push(head, 1);
head = push(head, 12);
head = push(head, 1);
head = push(head, 18);
head = push(head, 47);
head = push(head, 16);
head = push(head, 12);
head = push(head, 14);
head = push(head, 0);
// function to print the result
let res = check_pair_sum(head, 26);
if(res == false)
document.write("No pair found");
// this code is contributed by Kirti Agarwal
Time complexity: O(n ^ 2)
Auxiliary Space: O(n)
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