Merge pull request #1 from styxtheta/styxtheta-patch-1

implementation of hash tables in java

hash_table.java

@@ -0,0 +1,114 @@
+import java.util.Scanner;
+
+class HashTable
+{
+    int[] arr;
+    int capacity;
+
+    public HashTable(int capacity)
+    {
+        this.capacity = nextPrime(capacity);
+        arr = new int[this.capacity];
+    }
+
+    public void insert(int ele)
+    {
+        arr[ele % capacity] = ele;
+    }
+
+    public void clear()
+    {
+        arr = new int[capacity];
+    }
+
+    public boolean contains(int ele)
+    {
+        return arr[ele % capacity] == ele;
+    }
+
+    public void delete(int ele)
+    {
+        if (arr[ele % capacity] == ele)
+            arr[ele % capacity] = 0;
+        else
+            System.out.println("\nError : Element not found\n");
+    }
+
+    private static int nextPrime( int n )
+    {
+        if (n % 2 == 0)
+            n++;
+        for (; !isPrime(n); n += 2);
+
+        return n;
+    }
+
+    private static boolean isPrime(int n)
+    {
+        if (n == 2 || n == 3)
+            return true;
+        if (n == 1 || n % 2 == 0)
+            return false;
+        for (int i = 3; i * i <= n; i += 2)
+            if (n % i == 0)
+                return false;
+        return true;
+    }
+
+    public void printTable()
+    {
+        System.out.print("\nHash Table = ");
+        for (int i = 0; i < capacity; i++)
+            System.out.print(arr[i] +" ");
+        System.out.println();
+    }
+}
+
+public class HashTableTest
+{
+    public static void main(String[] args)
+    {
+        Scanner scan = new Scanner(System.in);
+        System.out.println("Hash Table Test\n\n");
+        System.out.println("Enter size");
+        HashTable ht = new HashTable(scan.nextInt() );
+
+        char ch;
+        do    
+        {
+            System.out.println("\nHash Table Operations\n");
+            System.out.println("1. insert ");
+            System.out.println("2. remove");
+            System.out.println("3. contains");            
+            System.out.println("4. clear");            
+
+            int choice = scan.nextInt();            
+            switch (choice)
+            {
+            case 1 : 
+                System.out.println("Enter integer element to insert");
+                ht.insert( scan.nextInt() ); 
+                break;                          
+            case 2 :                 
+                System.out.println("Enter integer element to delete");
+                ht.delete( scan.nextInt() ); 
+                break;                        
+            case 3 : 
+                System.out.println("Enter integer element to check if present");
+                System.out.println("Contains : "+ ht.contains(scan.nextInt() ));
+                break;                                   
+            case 4 : 
+                ht.clear();
+                System.out.println("Hash Table Cleared\n");
+                break;
+            default : 
+                System.out.println("Wrong Entry \n ");
+                break;   
+            }
+            ht.printTable();  
+
+            System.out.println("\nDo you want to continue (Type y or n) \n");
+            ch = scan.next().charAt(0);                        
+        } while (ch == 'Y'|| ch == 'y');  
+    }
+}