Added quick sort doubly linked list c++

Algorithms/Algorithms/Sorting/QuickSortDoublyLinkedList.cpp

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+// A C++ program to sort a linked list using Quicksort 
+#include <bits/stdc++.h> 
+using namespace std; 
+
+/* a node of the doubly linked list */
+class Node 
+{ 
+	public: 
+	int data; 
+	Node *next; 
+	Node *prev; 
+}; 
+
+/* A utility function to swap two elements */
+void swap ( int* a, int* b ) 
+{ int t = *a; *a = *b; *b = t; } 
+
+// A utility function to find 
+// last node of linked list 
+Node *lastNode(Node *root) 
+{ 
+	while (root && root->next) 
+		root = root->next; 
+	return root; 
+} 
+
+/* 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; 
+
+			swap(&(i->data), &(j->data)); 
+		} 
+	} 
+	i = (i == NULL)? l : i->next; // Similar to i++ 
+	swap(&(i->data), &(h->data)); 
+	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 *p = partition(l, h); 
+		_quickSort(l, p->prev); 
+		_quickSort(p->next, h); 
+	} 
+} 
+
+// The main function to sort a linked list. 
+// It mainly calls _quickSort() 
+void quickSort(Node *head) 
+{ 
+	// Find last node 
+	Node *h = lastNode(head); 
+
+	// Call the recursive QuickSort 
+	_quickSort(head, h); 
+} 
+
+// A utility function to print contents of arr 
+void printList(Node *head) 
+{ 
+	while (head) 
+	{ 
+		cout << head->data << " "; 
+		head = head->next; 
+	} 
+	cout << endl; 
+} 
+
+/* Function to insert a node at the 
+beginging of the Doubly Linked List */
+void push(Node** head_ref, int new_data) 
+{ 
+	Node* new_node = new Node; /* allocate node */
+	new_node->data = new_data; 
+
+	/* since we are adding at the 
+	beginning, prev is always NULL */
+	new_node->prev = NULL; 
+
+	/* link the old list off the new node */
+	new_node->next = (*head_ref); 
+
+	/* change prev of head node to new node */
+	if ((*head_ref) != NULL) (*head_ref)->prev = new_node ; 
+
+	/* move the head to point to the new node */
+	(*head_ref) = new_node; 
+} 
+
+/* Driver code */
+int main() 
+{ 
+	Node *a = NULL; 
+	push(&a, 5); 
+	push(&a, 20); 
+	push(&a, 4); 
+	push(&a, 3); 
+	push(&a, 30); 
+
+	cout << "Linked List before sorting \n"; 
+	printList(a); 
+
+	quickSort(a); 
+
+	cout << "Linked List after sorting \n"; 
+	printList(a); 
+
+	return 0; 
+} 
+
+
+