All Your Base - GCJ 2009

AllYourBase.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.math.BigInteger;
import java.io.*;

public class AllYourBase {  
  public BigInteger convert(String str) {
    BigInteger res = new BigInteger("0");
    int base = 0;
    int len = str.length();

    HashMap<String, Integer> hm = new HashMap<String, Integer>();
    int index = 1;

    for(int i=0;i<len;i++) {
      if(!hm.containsKey("" + str.charAt(i))) {
        if(i != 0) {
          if(index == 1) {
            index--;
          } else if (index == 0) {
            index = 2;
          } else {
            index++;
          }
        }        

        hm.put("" + str.charAt(i), new Integer(index));
        base++;
      }
    }

    if(hm.size() == 1) base = 2;
    System.out.println("base : " + base + " Len : " + len);

    for(int i=0;i<len;i++) {
      String s = str.charAt(i) + "";
      res = res.add(new BigInteger("" + hm.get(s)).multiply(new BigInteger("" + base).pow(len-i-1)));
    }

    return res;
  }  
}