Following is a typical recursive implementation of QuickSort for arrays. The implementation uses last element as pivot.
Can we use the same algorithm for Linked List?
Following is C++ implementation for the doubly linked list. The idea is simple, we first find out pointer to the last node. Once we have a pointer to the last node, we can recursively sort the linked list using pointers to first and last nodes of a linked list, similar to the above recursive function where we pass indexes of first and last array elements. The partition function for a linked list is also similar to partition for arrays. Instead of returning index of the pivot element, it returns a pointer to the pivot element. In the following implementation, quickSort() is just a wrapper function, the main recursive function is _quickSort() which is similar to quickSort() for array implementation.
Linked List before sorting 30 3 4 20 5 Linked List after sorting 3 4 5 20 30
Time Complexity: Time complexity of the above implementation is same as time complexity of QuickSort() for arrays. It takes O(n^2) time in the worst case and O(nLogn) in average and best cases. The worst case occurs when the linked list is already sorted.
Can we implement random quicksort for a linked list?
Quicksort can be implemented for Linked List only when we can pick a fixed point as the pivot (like the last element in the above implementation). Random QuickSort cannot be efficiently implemented for Linked Lists by picking random pivot.
The above implementation is for a doubly linked list. Modify it for a singly linked list. Note that we don’t have prev pointer in a singly linked list.
Refer QuickSort on Singly Linked List for solution.
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- XOR Linked List – A Memory Efficient Doubly Linked List | Set 2
- Difference between Singly linked list and Doubly linked list
- QuickSort on Singly Linked List
- Construct a Doubly linked linked list from 2D Matrix
- Memory efficient doubly linked list
- Delete a node in a Doubly Linked List
- Convert a given Binary Tree to Doubly Linked List | Set 1
- Convert a given Binary Tree to Doubly Linked List | Set 2
- Extract Leaves of a Binary Tree in a Doubly Linked List
- Convert a given Binary Tree to Doubly Linked List | Set 3
- Merge Sort for Doubly Linked List
- Convert a given Binary Tree to Doubly Linked List | Set 4
- Convert a Binary Tree into Doubly Linked List in spiral fashion
- Create a Doubly Linked List from a Ternary Tree
- Check if a doubly linked list of characters is palindrome or not
- Doubly Circular Linked List | Set 1 (Introduction and Insertion)
- Doubly Circular Linked List | Set 2 (Deletion)
- Convert a given Binary Tree to Circular Doubly Linked List | Set 2
- Insertion Sort for Doubly Linked List