mergesort LL

Author: sachuverma

DSA Crack Sheet/README.md

@@ -136,7 +136,7 @@
 - [Intersection of two sorted Linked lists](https://practice.geeksforgeeks.org/problems/intersection-of-two-sorted-linked-lists/1# "view question") - [Cpp Solution](./solutions/Intersection%20of%20two%20sorted%20Linked%20lists.cpp)
 - [Intersection Point in Y Shapped Linked Lists](https://practice.geeksforgeeks.org/problems/intersection-point-in-y-shapped-linked-lists/1 "view question") - [Cpp Solution](./solutions/Intersection%20Point%20in%20Y%20Shapped%20Linked%20Lists.cpp)
 - [Middle of the Linked List](https://leetcode.com/problems/middle-of-the-linked-list/ "view question") - [Cpp Solution](./solutions/Middle%20of%20the%20Linked%20List.cpp)
-- []( "view question") - [Cpp Solution](./solutions/.cpp)
+- [Merge Sort for Linked List](https://practice.geeksforgeeks.org/problems/sort-a-linked-list/1# "view question") - [Cpp Solution](./solutions/Merge%20Sort%20for%20Linked%20List.cpp)
 - []( "view question") - [Cpp Solution](./solutions/.cpp)
 
 ### Binary Tree

DSA Crack Sheet/solutions/Merge Sort for Linked List.cpp

@@ -0,0 +1,99 @@
+/*
+Merge Sort for Linked List
+==========================
+
+Given Pointer/Reference to the head of the linked list, the task is to Sort the given linked list using Merge Sort.
+Note: If the length of linked list is odd, then the extra node should go in the first list while splitting.
+
+Example 1:
+Input:
+N = 5
+value[]  = {3,5,2,4,1}
+Output: 1 2 3 4 5
+Explanation: After sorting the given
+linked list, the resultant matrix
+will be 1->2->3->4->5.
+
+Example 2:
+Input:
+N = 3
+value[]  = {9,15,0}
+Output: 0 9 15
+Explanation: After sorting the given
+linked list , resultant will be
+0->9->15.
+Your Task:
+For C++ and Python: The task is to complete the function mergeSort() which sort the linked list using merge sort function.
+For Java: The task is to complete the function mergeSort() and return the node which can be used to print the sorted linked list.
+
+Expected Time Complexity: O(N*Log(N))
+Expected Auxiliary Space: O(N)
+
+Constraints:
+1 <= T <= 100
+1 <= N <= 105
+*/
+
+Node *midNode(Node *head)
+{
+  auto fast = head, slow = head;
+  while (fast && fast->next)
+  {
+    fast = fast->next->next;
+    slow = slow->next;
+  }
+  return slow;
+}
+
+Node *merge(Node *head1, Node *head2)
+{
+  Node *ans = new Node(-1);
+  auto temp = ans, temp1 = head1, temp2 = head2;
+
+  while (temp1 && temp2)
+  {
+    if (temp1->data < temp2->data)
+    {
+      auto next = temp1->next;
+      temp->next = temp1;
+      temp1->next = NULL;
+      temp = temp->next;
+      temp1 = next;
+    }
+    else
+    {
+      auto next = temp2->next;
+      temp->next = temp2;
+      temp2->next = NULL;
+      temp = temp->next;
+      temp2 = next;
+    }
+  }
+
+  if (temp1)
+    temp->next = temp1;
+  if (temp2)
+    temp->next = temp2;
+
+  return ans->next;
+}
+
+Node *mergeSort(Node *head)
+{
+  if (!head || !head->next)
+    return head;
+
+  auto mid = midNode(head);
+  auto temp = head;
+
+  while (temp->next != mid)
+    temp = temp->next;
+  temp->next = NULL;
+
+  auto head2 = mid;
+
+  head = mergeSort(head);
+  head2 = mergeSort(head2);
+
+  return merge(head, head2);
+}