Java Program For QuickSort On Doubly Linked List
Last Updated :
03 May, 2023
Following is a typical recursive implementation of QuickSort for arrays. The implementation uses last element as pivot.
Java
/* A typical recursive implementation of
Quicksort for array*/
/* This function takes last element as pivot,
places the pivot element at its correct
position in sorted array, and places all
smaller (smaller than pivot) to left of
pivot and all greater elements to right
of pivot */
static int partition (int []arr, int l, int h)
{
int x = arr[h];
int i = (l - 1);
for(int j = l; j <= h - 1; j++)
{
if (arr[j] <= x)
{
i++;
int tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
}
int tmp = arr[i + 1];
arr[i + 1] = arr[h];
arr[h] = tmp;
return(i + 1);
}
/* A[] --> Array to be sorted,
l --> Starting index,
h --> Ending index */
static void quickSort(int []A, int l,
int h)
{
if (l < h)
{
// Partitioning index
int p = partition(A, l, h);
quickSort(A, l, p - 1);
quickSort(A, p + 1, h);
}
}
// This code is contributed by pratham76.
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.
Java
// A Java program to sort a linked list using Quicksort
class QuickSort_using_Doubly_LinkedList{
Node head;
/* a node of the doubly linked list */
static class Node{
private int data;
private Node next;
private Node prev;
Node(int d){
data = d;
next = null;
prev = null;
}
}
// A utility function to find last node of linked list
Node lastNode(Node node){
while(node.next!=null)
node = node.next;
return node;
}
/* Considers last element as pivot, places the pivot element at its
correct position in sorted array, and places all smaller (smaller than
pivot) to left of pivot and all greater elements to right of pivot */
Node partition(Node l,Node h)
{
// set pivot as h element
int x = h.data;
// similar to i = l-1 for array implementation
Node i = l.prev;
// Similar to "for (int j = l; j <= h- 1; j++)"
for(Node j=l; j!=h; j=j.next)
{
if(j.data <= x)
{
// Similar to i++ for array
i = (i==null) ? l : i.next;
int temp = i.data;
i.data = j.data;
j.data = temp;
}
}
i = (i==null) ? l : i.next; // Similar to i++
int temp = i.data;
i.data = h.data;
h.data = temp;
return i;
}
/* A recursive implementation of quicksort for linked list */
void _quickSort(Node l,Node h)
{
if(h!=null && l!=h && l!=h.next){
Node temp = partition(l,h);
_quickSort(l,temp.prev);
_quickSort(temp.next,h);
}
}
// The main function to sort a linked list. It mainly calls _quickSort()
public void quickSort(Node node)
{
// Find last node
Node head = lastNode(node);
// Call the recursive QuickSort
_quickSort(node,head);
}
// A utility function to print contents of arr
public void printList(Node head)
{
while(head!=null){
System.out.print(head.data+" ");
head = head.next;
}
}
/* Function to insert a node at the beginning of the Doubly Linked List */
void push(int new_Data)
{
Node new_Node = new Node(new_Data); /* allocate node */
// if head is null, head = new_Node
if(head==null){
head = new_Node;
return;
}
/* link the old list of the new node */
new_Node.next = head;
/* change prev of head node to new node */
head.prev = new_Node;
/* since we are adding at the beginning, prev is always NULL */
new_Node.prev = null;
/* move the head to point to the new node */
head = new_Node;
}
/* Driver program to test above function */
public static void main(String[] args){
QuickSort_using_Doubly_LinkedList list = new QuickSort_using_Doubly_LinkedList();
list.push(5);
list.push(20);
list.push(4);
list.push(3);
list.push(30);
System.out.println("Linked List before sorting ");
list.printList(list.head);
System.out.println("
Linked List after sorting");
list.quickSort(list.head);
list.printList(list.head);
}
}
// This code has been contributed by Amit Khandelwal
Output :
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.
Space Complexity: O(n). The extra space is due to the function call stack.
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.
Please refer complete article on QuickSort on Doubly Linked List for more details!
Similar Reads
DSA Tutorial - Learn Data Structures and Algorithms DSA (Data Structures and Algorithms) is the study of organizing data efficiently using data structures like arrays, stacks, and trees, paired with step-by-step procedures (or algorithms) to solve problems effectively. Data structures manage how data is stored and accessed, while algorithms focus on
7 min read
Quick Sort QuickSort is a sorting algorithm based on the Divide and Conquer that picks an element as a pivot and partitions the given array around the picked pivot by placing the pivot in its correct position in the sorted array. It works on the principle of divide and conquer, breaking down the problem into s
12 min read
Merge Sort - Data Structure and Algorithms Tutorials Merge sort is a popular sorting algorithm known for its efficiency and stability. It follows the divide-and-conquer approach. It works by recursively dividing the input array into two halves, recursively sorting the two halves and finally merging them back together to obtain the sorted array. Merge
12 min read
Data Structures Tutorial Data structures are the fundamental building blocks of computer programming. They define how data is organized, stored, and manipulated within a program. Understanding data structures is very important for developing efficient and effective algorithms. What is Data Structure?A data structure is a st
2 min read
Bubble Sort Algorithm Bubble Sort is the simplest sorting algorithm that works by repeatedly swapping the adjacent elements if they are in the wrong order. This algorithm is not suitable for large data sets as its average and worst-case time complexity are quite high.We sort the array using multiple passes. After the fir
8 min read
Breadth First Search or BFS for a Graph Given a undirected graph represented by an adjacency list adj, where each adj[i] represents the list of vertices connected to vertex i. Perform a Breadth First Search (BFS) traversal starting from vertex 0, visiting vertices from left to right according to the adjacency list, and return a list conta
15+ min read
Binary Search Algorithm - Iterative and Recursive Implementation Binary Search Algorithm is a searching algorithm used in a sorted array by repeatedly dividing the search interval in half. The idea of binary search is to use the information that the array is sorted and reduce the time complexity to O(log N). Binary Search AlgorithmConditions to apply Binary Searc
15 min read
Insertion Sort Algorithm Insertion sort is a simple sorting algorithm that works by iteratively inserting each element of an unsorted list into its correct position in a sorted portion of the list. It is like sorting playing cards in your hands. You split the cards into two groups: the sorted cards and the unsorted cards. T
9 min read
Array Data Structure Guide In this article, we introduce array, implementation in different popular languages, its basic operations and commonly seen problems / interview questions. An array stores items (in case of C/C++ and Java Primitive Arrays) or their references (in case of Python, JS, Java Non-Primitive) at contiguous
3 min read
Sorting Algorithms A Sorting Algorithm is used to rearrange a given array or list of elements in an order. For example, a given array [10, 20, 5, 2] becomes [2, 5, 10, 20] after sorting in increasing order and becomes [20, 10, 5, 2] after sorting in decreasing order. There exist different sorting algorithms for differ
3 min read