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Encoder.java

package com.ghosthack.turismo.util;


public class Encoder
{
  protected static final String DEFAULT_ALPHABET = "ed82j6rhkyf5amu9x4qbgpstn7vc3w1ioz";
  protected static final int DEFAULT_BLOCK_SIZE = 22;
  private String alphabet;
  private int blockSize;
  private int mask;
  private int[] mapping;
  
  public Encoder()
  {
    this.alphabet = DEFAULT_ALPHABET;
    this.blockSize = DEFAULT_BLOCK_SIZE;
    this.mask = (1 << blockSize) - 1;
    this.mapping = new int[blockSize];
    for(int i = 0; i<blockSize; i++) {
      mapping[i] = blockSize-i-1;
    }
  }
  
  public static void main(String[] args)
  {
    for(int i = 1; i<10; i++) {
      System.out.println(new Encoder().toKey(i));
    }
  }
  
  public String toKey(int id) {
    return enbase(encode(id));
  }

  private String enbase(int n)
  {
    return enbase(n, 0);
  }

  private String enbase(int n, int minLength)
  {
    String result = _enbase(n);
    StringBuilder sb = new StringBuilder();
    int a = minLength - result.length();
    if(a > 0) {
      for(int i=0; i<a; i++) {
        sb.append(alphabet.charAt(0));
      }
    }
    String padding = sb.toString();
    return String.format("%s%s", padding, result);
  }

  private String _enbase(int x)
  {
    int n = alphabet.length();
    if(x < n) {
      return alphabet.charAt(x)+"";
    }
    return enbase(x/n) + alphabet.charAt(x%n);
  }

  private int encode(int n)
  {
    return (n & ~mask) | _encode(n & mask);
  }

  private int _encode(int n)
  {
    int result = 0;
    for(int i = 0; i<mapping.length; i++) {
      int b = mapping[i];
      if((n & (1<<i)) != 0) {
        result |= (1 << b);
      }
    }
    return result;
  }
  
}