Clock Puzzle from JAVALOBBY (dzone)

Here is one of the latest java puzzle from dzone javalobby.

HowMany 1's Appear in A Binary Clock Across an Entire Day 

 import org.apache.commons.lang.StringUtils;

 import com.google.common.base.Function;

 public class ClockPuzzle {

       public Function<Integer, Integer> countOnes = new Function<Integer, Integer>() {

              public Integer apply(Integer number) {

                     String binaryString = Integer.toBinaryString(number);

                     return StringUtils.countMatches(binaryString, "1");

              }

       };

       public long countOnesInOneDay() {

              long onesOccurrences = 0;

              for (int hour = 0; hour < 24; hour++) {

                     for (int minute = 0; minute < 60; minute++) {

                           for (int second = 0; second < 60; second++) {

                                  onesOccurrences += countOnes.apply(hour)

                                  + countOnes.apply(minute) +  countOnes.apply(second);

                           }

                     }

              }

              return onesOccurrences;

       }

 }

 import static org.junit.Assert.assertTrue;

 import org.apache.log4j.Logger;

 import org.junit.Test;

 public class ClockPuzzleTest {

      

       public static final Logger logger = Logger.getLogger(ClockPuzzleTest.class);

      

       ClockPuzzle clock = new ClockPuzzle();

       @Test

       public void shouldCoutOnes() {

              assertTrue(clock.countOnes.apply(6) == 2);

              assertTrue(clock.countOnes.apply(7) == 3);

              assertTrue(clock.countOnes.apply(8) == 1);

       }

       @Test

       public void shouldCoutOnesInOneDay() {

              logger.info("From " + hourStart + " To " + hourEnd + " contains "

                           + clock.countOnesInOneDay() + " ones.");

       }

 }