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Sort_a_K-sorted_DLL.cpp
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Sort_a_K-sorted_DLL.cpp
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/*
Problem Statement:
-----------------
Given a doubly linked list containing n nodes, where each node is at most k away from its target position in the list. The problem is to sort the given doubly linked list.
For example, let us consider k is 2, a node at position 7 in the sorted doubly linked list, can be at positions 5, 6, 7, 8, 9 in the given doubly linked list.
Example:
-------
Input : DLL: 3 <-> 6 <-> 2 <-> 12 <-> 56 <-> 8
K = 2.
Output : DLL : 2 <-> 3 <-> 6 <-> 8 <-> 12 <-> 56
*/
// Link --> https://www.geeksforgeeks.org/sort-k-sorted-doubly-linked-list/
// Code:
#include <bits/stdc++.h>
using namespace std;
struct Node
{
int data;
struct Node* next, *prev;
};
void insert(struct Node** head, int data)
{
Node* temp = new Node;
temp->data = data;
temp->next = temp->prev = NULL;
if((*head) == NULL)
(*head) = temp;
else
{
temp->next = *head;
(*head)->prev = temp;
(*head) = temp;
}
}
void printList(struct Node* head)
{
if(head == NULL)
return;
while(head != NULL)
{
cout<<head->data<<" ";
head = head->next;
}
}
struct compare
{
bool operator()(Node* p1 , Node* p2)
{
return p1->data > p2->data;
}
};
Node* sortKDLL(Node* head , int k)
{
if(head == NULL)
return head;
priority_queue <Node* , vector<Node*> , compare> pq;
Node* newHead = NULL , *last;
for(int i=0 ; head != NULL && i<=k ; i++)
{
pq.push(head);
head = head->next;
}
while(!pq.empty())
{
if(newHead == NULL)
{
newHead = pq.top();
newHead->prev = NULL;
last = newHead;
}
else
{
last->next = pq.top();
pq.top()->prev = last;
last = pq.top();
}
pq.pop();
if(head != NULL)
{
pq.push(head);
head = head->next;
}
}
last->next = NULL;
return newHead;
}
int main()
{
Node* head = NULL;
insert(&head, 8);
insert(&head, 56);
insert(&head, 12);
insert(&head, 2);
insert(&head, 6);
insert(&head, 3);
cout<<"Initially DLL is : ";
printList(head);
int k = 2;
Node *answer = sortKDLL(head , k);
cout<<"\n\nDLL after sorting is : ";
printList(answer);
return 0;
}