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Flattening a Linked list in C++
In this problem, we are given linked list consisting of two pointer nodes, right and down.
Right node is the main linked list pointer.
Down node is for secondary linked list starting with that node.
All the linked lists are sorted.
Our task is to create a program to flatten a linked list and the resulting list will itself be a sorted one.
Let’s take an example to understand the problem
Input
Output
1-> 9-> 8 -> 4 -> 6-> 7-> 2-> 3-> 5
Solution Approach
A solution to the problem is using merge sort for a linked list. This method will merge the lists recursively in a sorted order to form a flattened list.
Example
Program to illustrate the working of our solution
#include <bits/stdc++.h>
using namespace std;
class Node{
public:
int data;
Node *right, *down;
};
Node* head = NULL;
Node* mergeList(Node* a, Node* b){
if (a == NULL)
return b;
if (b == NULL)
return a;
Node* result;
if (a->data < b->data){
result = a;
result->down = mergeList(a->down, b);
}
else{
result = b;
result->down = mergeList(a, b->down);
}
result->right = NULL;
return result;
}
Node* flattenLinkedList(Node* root){
if (root == NULL || root->right == NULL)
return root;
root->right = flattenLinkedList(root->right);
root = mergeList(root, root->right);
return root;
}
Node* push(Node* head_ref, int data){
Node* new_node = new Node();
new_node->data = data;
new_node->right = NULL;
new_node->down = head_ref;
head_ref = new_node;
return head_ref;
}
int main(){
head = push(head, 7);
head = push(head, 1);
head->right = push(head->right, 11);
head->right = push(head->right, 5);
head->right = push(head->right, 4);
head->right->right = push(head->right->right, 12);
head->right->right = push(head->right->right, 6);
head->right->right->right = push(head->right->right->right, 8);
head->right->right->right->right = push(head->right->right->right->right, 16);
head = flattenLinkedList(head);
cout<<"The Flattened Linked list is : \n";
Node* temp = head;
while (temp != NULL){
cout<<temp->data<<" => ";
temp = temp->down;
}
cout<<"NULL";
return 0;
}Output
The Flattened Linked list is : 1 => 4 => 5 => 6 => 7 => 8 => 11 => 12 => 16 => NULL
Updated on: 01-Feb-2022
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