/**
 * A program to simulate caching.
 *
 * First write a method or function called calculateAnswer()
 * that takes an integer x as input and calculates (and returns)
 * the sum 1 + 2 + ... + x.
 *     (Pretend this method is computationally costly!)
 *
 * Initially, the cache is empty.  Ask the user to input a number
 * in the range 1..100.  If the answer is not in the cache, call
 * calculateAnswer() and display the resulting sum; also store the
 * result in the cache.  If the answer is in the cache, simply
 * display the answer.
 *
 */
import java.util.Scanner;

public class Caching
{
 // Do something computationally intensive
 public static int calculateAnswer( int x )
 {
   int sum = 0;

   for ( int y = 1 ; y <= x ; y++ ) {
     sum += y;
   }

   try { Thread.sleep( 3000 ); }
   catch( InterruptedException ex ) {  }

   return sum;
 }

 public static final int cacheSize = 10;

 public static void main( String[] args )
 {
   Scanner keyboard = new Scanner( System.in );

   int[] mapping = new int[ cacheSize ];
   int[] results = new int[ cacheSize ];

   while ( true )
   {
     System.out.print( "Enter x: " );
     int x = keyboard.nextInt();

     // Determine the cache index by dividing x by 10 and
     // using the remainder (which will be 0..9)
     int index = x % cacheSize;

     if ( mapping[ index ] != x )
     {
       // CACHE MISS
       int result = calculateAnswer( x );
       System.out.print( "==> " + result );

       // Store x and result in the cache, overwriting what
       // was previously in the cache at the given index
       mapping[ index ] = x;
       results[ index ] = result;
       System.out.println( " (stored in cache at index " + index + ")" );
     }
     else
     {
       // CACHE HIT!
       System.out.println( "==> " + results[ index ] + " (cache hit!)" );
     }
   }
 }

}