Given a linked list of 0s, 1s and 2s, sort it.
Examples:
Input: 1 -> 1 -> 2 -> 0 -> 2 -> 0 -> 1 -> NULL Output: 0 -> 0 -> 1 -> 1 -> 1 -> 2 -> 2 -> NULL Input: 1 -> 1 -> 2 -> 1 -> 0 -> NULL Output: 0 -> 1 -> 1 -> 1 -> 2 -> NULL
Source: Microsoft Interview | Set 1
Following steps can be used to sort the given linked list.
- Traverse the list and count the number of 0s, 1s, and 2s. Let the counts be n1, n2, and n3 respectively.
- Traverse the list again, fill the first n1 nodes with 0, then n2 nodes with 1, and finally n3 nodes with 2.
Below image is a dry run of the above approach:
Below is the implementation of the above approach:
Java
// Java program to sort a linked list // of 0, 1 and 2 class LinkedList
{ // Head of list
Node head;
// Linked list Node
class Node
{
int data;
Node next;
Node( int d)
{
data = d;
next = null ;
}
}
void sortList()
{
// Initialise count of 0 1
// and 2 as 0
int count[] = { 0 , 0 , 0 };
Node ptr = head;
/* Count total number of '0', '1' and '2'
count[0] will store total number of '0's
count[1] will store total number of '1's
count[2] will store total number of '2's */
while (ptr != null )
{
count[ptr.data]++;
ptr = ptr.next;
}
int i = 0 ;
ptr = head;
/* Let say count[0] = n1, count[1] = n2
and count[2] = n3
now start traversing list from head node,
1) fill the list with 0, till n1 > 0
2) fill the list with 1, till n2 > 0
3) fill the list with 2, till n3 > 0 */
while (ptr != null )
{
if (count[i] == 0 )
i++;
else {
ptr.data= i;
--count[i];
ptr = ptr.next;
}
}
}
// Utility functions
/* Inserts a new Node at front
of the list. */
public void push( int new_data)
{
/* 1 & 2: Allocate the Node &
Put in the data*/
Node new_node = new Node(new_data);
// 3. Make next of new Node as head
new_node.next = head;
// 4. Move the head to point to
// new Node
head = new_node;
}
// Function to print linked list
void printList()
{
Node temp = head;
while (temp != null )
{
System.out.print(temp.data + " " );
temp = temp.next;
}
System.out.println();
}
// Driver code
public static void main(String args[])
{
LinkedList llist = new LinkedList();
/* Constructed Linked List is
1->2->3->4->5->6->7->8->8->9->null */
llist.push( 0 );
llist.push( 1 );
llist.push( 0 );
llist.push( 2 );
llist.push( 1 );
llist.push( 1 );
llist.push( 2 );
llist.push( 1 );
llist.push( 2 );
System.out.println(
"Linked List before sorting" );
llist.printList();
llist.sortList();
System.out.println(
"Linked List after sorting" );
llist.printList();
}
} // This code is contributed by Rajat Mishra |
Output:
Linked List Before Sorting 2 1 2 1 1 2 0 1 0 Linked List After Sorting 0 0 1 1 1 1 2 2 2
Time Complexity: O(n) where n is the number of nodes in the linked list.
Auxiliary Space: O(1)
Please refer complete article on Sort a linked list of 0s, 1s and 2s for more details!