Merge sort is often preferred for sorting a linked list. The slow random-access performance of a linked list makes some other algorithms (such as quicksort) perform poorly, and others (such as heapsort) completely impossible.
Let head be the first node of the linked list to be sorted and headRef be the pointer to head. Note that we need a reference to head in MergeSort() as the below implementation changes next links to sort the linked lists (not data at the nodes), so head node has to be changed if the data at the original head is not the smallest value in the linked list.
MergeSort(headRef) 1) If the head is NULL or there is only one element in the Linked List then return. 2) Else divide the linked list into two halves. FrontBackSplit(head, &a, &b); /* a and b are two halves */ 3) Sort the two halves a and b. MergeSort(a); MergeSort(b); 4) Merge the sorted a and b (using SortedMerge() discussed here) and update the head pointer using headRef. *headRef = SortedMerge(a, b);
Sorted Linked List is: 2 3 5 10 15 20
Time Complexity: O(n Log n)
Please write comments if you find the above code/algorithm incorrect, or find better ways to solve the same problem.
Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.
- Why Quick Sort preferred for Arrays and Merge Sort for Linked Lists?
- Union and Intersection of two linked lists | Set-2 (Using Merge Sort)
- Difference of two Linked Lists using Merge sort
- Merge Sort with O(1) extra space merge and O(n lg n) time
- Merge two sorted linked lists
- Merge two sorted linked lists such that merged list is in reverse order
- In-place Merge two linked lists without changing links of first list
- Merge K sorted linked lists | Set 1
- Merge k sorted linked lists | Set 2 (Using Min Heap)
- Sorted merge of two sorted doubly circular linked lists
- Merge odd and even positioned nodes of two Linked Lists alternately
- Merge two unsorted linked lists to get a sorted list
- Quick Sort vs Merge Sort
- Merge Sort vs. Insertion Sort
- Merge Sort for Doubly Linked List
- Iterative Merge Sort for Linked List
- Merge a linked list into another linked list at alternate positions
- Merge operations using STL in C++ | merge(), includes(), set_union(), set_intersection(), set_difference(), ., inplace_merge,
- Construct a Maximum Sum Linked List out of two Sorted Linked Lists having some Common nodes