Google Code Jam: Alien Numbers Solution

The problem definition could be found at Code Jam web site.

Idea

• get sequence_number of a alien_number in source alien_language
• by a sequence_number get alien_number in target alien_language

My solution is published below.
Main function is solve.

public class AlienNumbers {
   
    private Scanner scanner;
    private PrintWriter writer;
   
   ...
   
    public AlienNumbers(InputStream is, OutputStream os) {
        scanner = new Scanner(is);
        writer = new PrintWriter(os);
    }
   
   ...
   
    /**
     * Solve the problem
     */
    public void solve() {
        int n = scanner.nextInt();
   
        for (int i = 1; i <= n; i++) {
            writer.print("Case #");
            writer.print(i + ": ");
   
            char[] alienNumber = scanner.next().toCharArray();
            char[] sourceLanguage = scanner.next().toCharArray();
            char[] targetLanguage = scanner.next().toCharArray();
   
            // long is enough to store sequence number
            // see Long.MAX_VALUE (9223372036854775807 ~ 10^19)
            long sequenceNumber = getSequenceNumber(alienNumber, sourceLanguage);
            char target[] = getAlienNumber(sequenceNumber, targetLanguage);
   
            writer.println(target);
        }
    }
   
    /**
     * Gets sequence number of a alien_number in alien language
     *
     * @param alienNumber   alien number
     * @param alienLanguage alien language
     * @return sequence number
     */
    private long getSequenceNumber(char[] alienNumber, char[] alienLanguage) {
        long result = 0;
        for (int i = 0; i < alienNumber.length; i++) {
            for (int j = 0; j < alienLanguage.length; j++) {
                if (alienNumber[alienNumber.length - i - 1] == alienLanguage[j]) {
                    result += (long) Math.pow(alienLanguage.length, i) * j;
                    break;
                }
            }
        }
        return result;
    }
   
    /**
     * Gets alien_number by a sequence number in alien language
     *
     * @param sequenceNumber sequence number
     * @param alienLanguage  alien language
     * @return alien number
     */
    private char[] getAlienNumber(long sequenceNumber, char[] alienLanguage) {
        StringBuilder alienNumber = new StringBuilder();
   
        for (int i = (int) log(sequenceNumber, alienLanguage.length); i >= 0; i--) {
            long power = (long) Math.pow(alienLanguage.length, i);
            int index = (int) (sequenceNumber / power);
            alienNumber.append(alienLanguage[index]);
            sequenceNumber -= index * power;
        }
        return alienNumber.toString().toCharArray();
    }
   
    /**
     * Base based logarithm of number
     *
     * @param number number
     * @param base   base
     * @return logarithm
     */
    private long log(long number, long base) {
        return (long) (Math.log(number) / Math.log(base));
    }
}

See also other posts in Code Jam