Linked List Pair Sum

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



C++

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// 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 off 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;
}

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Java

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// 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 conlinked 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

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Python3

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# 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 off 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

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C#

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// 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 conlinked 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

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Output:

14 12

Time complexity:O(n*n)

Method 2 (using hashing)
1. Take a hashtable and mark all element with zero
2. Iteratively mark all the element as 1 in hashtable which are present in linked list
3. Iteratively find sum-current element of linked list is present in hashtable or not

C++

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// 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 off 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;
}

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Java

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// 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 off 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 conlinked 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 

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C#

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// 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 off 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 conlinked 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

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Output:

14 12

Time complexity : O(n)
Auxiliary Space : O(n)



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