Create TelephoneDirectory

Author: nkatre

TelephoneDirectory

@@ -0,0 +1,120 @@
+/*
+
+Problem
+
+
+You will have to design a telephone directory where the following operations would be supported.
+1. GET: It will provide a number which is not assigned to anyone
+2. CHECK: Given a number it will tell whether it is assigned to anyone or not
+3. RELEASE: It will recycle or release a number
+
+*/
+
+public class TelephoneDirectory
+{
+ public static void main(String[] args)
+ {
+  Directory directory = new Directory(5);
+  int number1 = directory.getAvailableNumber();
+  System.out.println(number1);
+  int number2 = directory.getAvailableNumber();
+  System.out.println(number2);
+  System.out.println(directory.isAvailable(3));
+  int number3 = directory.getAvailableNumber();
+  System.out.println(number3);
+  System.out.println(directory.isAvailable(3));
+  int number4 = directory.getAvailableNumber();
+  System.out.println(directory.isAvailable(3));
+  System.out.println(number4);
+  int number5 = directory.getAvailableNumber();
+  System.out.println(number5);
+  int number6 = directory.getAvailableNumber();
+  System.out.println(number6);
+  int number7 = directory.getAvailableNumber();
+  System.out.println(number7);
+  directory.release(3);
+  System.out.println(directory.isAvailable(3));
+  int number8 = directory.getAvailableNumber();
+  System.out.println(number8);
+  System.out.println(directory.isAvailable(3));
+ }
+
+ private static class Directory
+ {
+  Node[] nodes;
+  Node head;
+
+  public Directory(int maxNumbers)
+  {
+   nodes = new Node[maxNumbers];
+   for (int i = 0; i < maxNumbers; ++i)
+   {
+    nodes[i] = new Node(i);
+    if (i != 0)
+    {
+     nodes[i].previous = nodes[i - 1];
+     nodes[i - 1].next = nodes[i];
+    }
+   }
+   nodes[maxNumbers - 1].next = nodes[0];
+   nodes[0].previous = nodes[maxNumbers - 1];
+   head = nodes[0];
+  }
+
+  public int getAvailableNumber()
+  {
+   if (head == null)
+    return -1;
+   int temp = head.number;
+   head.available = false;
+   if (head.next == head)
+    head = null;
+   else
+   {
+    head.previous.next = head.next;
+    head.next.previous = head.previous;
+    head = head.next;
+   }
+   return temp;
+  }
+
+  public boolean isAvailable(int number)
+  {
+   return nodes[number].available;
+  }
+
+  public void release(int number)
+  {
+   if (nodes[number].available == false)
+   {
+    nodes[number].available = true;
+    if (head == null)
+    {
+     head = nodes[number];
+     nodes[number].next = nodes[number];
+     nodes[number].previous = nodes[number];
+    } else
+    {
+     nodes[number].next = head.next;
+     nodes[number].previous = head;
+     head.next.previous = nodes[number];
+     head.next = nodes[number];
+    }
+   }
+  }
+
+  private static class Node
+  {
+   boolean available = true;
+   Node next;
+   Node previous;
+   int number;
+
+   public Node(int number)
+   {
+    this.number = number;
+   }
+  }
+ }
+
+}