gistfile1.java

public class OnesFunction {

  private static LoadingCache<Integer, Integer> cache = CacheBuilder
			.newBuilder().maximumSize(1000)
			.expireAfterAccess(10, TimeUnit.MINUTES)
			.build(new CacheLoader<Integer, Integer>() {
				@Override
				public Integer load(final Integer i) throws ExecutionException {
					return countOnes(i);
				}
			});

	/**
	 * @param args
	 * @throws ExecutionException 
	 */
	public static void main(String[] args) throws ExecutionException {
		int i = 2;
		while (true) {
			final int n = countOnes(i);
			System.out.println("" + i + ":" + n);
			if (i == n)
				break;
			i++;
		}
	}

	public static int countOnes(final int i) throws ExecutionException {
		if (i == 0)
			return 0;
		return internalCountOnes(i) + cache.get(i - 1);
	}

	private static int internalCountOnes(final int i) {
		final String s = String.valueOf(i);
		int sum = 0;
		for (final char c : s.toCharArray())
			if (c == '1')
				sum += 1;
		return sum;
	}

}