Sunday 22 May 2016

Find Length of a Linked List (Iterative and Recursive)

Function to find the length of Linked list.

Recursive Solution:
int getLengthRecur (start)
1) if start is NULL, return 0.
2) else return 1 + getLengthRecur (start->next)

Iterative solution:
1) Initialize count as 0
2) Initialize a node pointer, current = start.
3) Repeat while current is not NULL
     a) current = current -> next
     b) count++;
4) Return count

Java code for both approaches:

/** Linked list Node*/
class Node {
   int data;
   Node next;
   Node(int d)  {
      data = d;
      next = null;
   }
}

/**
 * @author rajesh.kumar
 */
class LinkedList {
   Node start;

   /**
    * Inserts a new Node at front of the list.
    * @param value
    */
   public void add(int value) {
      /* 1 & 2: Allocate the Node & Put in the data*/
      Node nNode = new Node(value);

      /* 3. Make next of new Node as head */
      nNode.next = start;

      /* 4. Move the head to point to new Node */
      start = nNode;
   }

   /** Returns count of nodes in linked list */
   public int getLengthIter() {
      Node temp = start;
      int count = 0;
      while (temp != null) {
         count++;
         temp = temp.next;
      }
      return count;
   }

   private int getLengthRecur() {
      Node node = start;
      if(node!=null) {
         return 1+getLengthRecur(node.next);  
      } else {
         return 0;
      }
   }

   private int getLengthRecur(Node node) {
      if(node!=null) {
         return 1+getLengthRecur(node.next);
      } else {
         return 0;
      }
   }

   public static void main(String[] args) {

      LinkedList list = new LinkedList();
      list.add(1);
      list.add(2);
      list.add(3);
      list.add(4);
      list.add(5);

      System.out.println("Ietrative Length #" + list.getLengthIter());

      System.out.println("Recursive Length #" + list.getLengthRecur());
   }
}

Output:
     Ietrative Length #5
     Recursive Length #5

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