When Is Cheryl's Birthday

大早上起来逛微博，看见@西瓜大丸子汤Po的一个逻辑题，遂点开看之...

原文链接：http://nbviewer.ipython.org/url/norvig.com/ipython/Cheryl.ipynb

然后发现这不是TM的猜卡牌的那个题么，某次面试的时候还跪了来着。。接着就魔性大发，试着用JAVA来学习一下

 package cn.edu.bipt.hcol;

 import java.util.ArrayList;
 import java.util.List;

 /**
  * This logic puzzle has been making the rounds:
  *
  * Albert and Bernard just became friends with Cheryl, and they want to know
  * when her birtxhday is. Cheryl gave them a list of 10 possible dates:
  *
  * May 15 May 16 May 19 June 17 June 18 July 14 July 16 August 14 August 15
  * August 17 Cheryl then tells Albert and Bernard separately the month and the
  * day of the birthday respectively.
  *
  * Albert: I don't know when Cheryl's birthday is, but I know that Bernard does
  * not know too.
  *
  * Bernard: At first I don't know when Cheryl's birthday is, but I know now.
  *
  * Albert: Then I also know when Cheryl's birthday is.
  *
  * So when is Cheryl's birthday?
  *
  * @author Colin
  *
  */
 public class WhenIsCherylsBirthday {

     public static final String DATES[] = { "May 15", "May 16", "May 19",
             "June 17", "June 18", "July 14", "July 16", "August 14",
             "August 15", "August 17" };

     /**
      * Albert : I don't know when Cheryl's birthday is, but I know that Bernard
      * does not know too.
      *
      * That means: Albert : After Cheryl told me the month of her birthdate, I
      * didn't know her birthday, I don't know which day Cheryl told Bernard, but
      * I know that for all of the possible dates, if Bernard is told that day ,
      * he wouldn't know the birthdate.
      *
      */
     private boolean statement3(String date) {
         // When Cheryl told the month to Albert
         // Albert : I know if Bernard doesn't knows Cheryl birthday when Cheryl
         // told him the day
         // that means the day is not unique in DATES
         // that means I know the month and I know the days but Bernard doesn't
         // konws
         boolean temper = true;

         List<String> possible_dates = tell(getMonth(date));

         for (int i = 0; i < possible_dates.size(); i++) {
             if (know(tell(getDay(possible_dates.get(i))))) {
                 temper = false;
                 break;
             }
         }

         return !know(possible_dates) && temper;
     }

     /**
      * Bernard: At first I don't know when Cheryl's birthday is, but I know now.
      *
      * Bernard: At first time Cheryl told me the day,and i didn't know. Then I
      * considered just the dates for which Albert's statement3 is true,and now I
      * know.
      *
      * @param date
      * @return
      */
     private boolean statement4(String date) {
         List<String> atFirst = tell(getDay(date));

         List<String> filterItem = new ArrayList<String>();
         for (String item : atFirst) {
             if (statement3(item) == true)
                 filterItem.add(item);
         }

         return !know(atFirst) && know(filterItem);
     }

     /**
      * Albert: Then I also know when Cheryl's birthday is.
      *
      * @param date
      * @return
      */
     private boolean statement5(String date) {
         List<String> mList = tell(getMonth(date));

         List<String> filterItem = new ArrayList<String>();
         for (String item : mList) {
             if (true == statement4(item))
                 filterItem.add(item);
         }

         return know(filterItem);
     }

     /**
      * filter(statement4 , filter(statement3 , DATES)) filter(statement4 ,
      * tell(getMonth(date)))
      *
      * @param date
      * @return
      */
     private boolean statement3to5(String date) {
         return statement3(date) && statement4(date) && statement5(date);
     }

     private String getCherylsBirthday(String dates[]) {
         String birthday = "";
         for (String date : dates) {
             if (true == statement3to5(date))
                 birthday = date;
         }
         return birthday;
     }

     /**
      * Cheryl tells a part of birthday to someone; Return a new list of possible
      * dates that match the part.
      *
      * @param part
      * @param return
      */
     private List<String> tell(String part) {
         List<String> mList = new ArrayList<String>();
         char c = part.charAt(0);

         // 匹配“月”
         if (c >= 'A' && c <= 'Z') {
             for (String date : DATES) {
                 if (part.equals(getMonth(date))) {
                     mList.add(date);
                 }
             }
         } else {// 匹配“日”
             for (String date : DATES) {
                 if (part.equals(getDay(date))) {
                     mList.add(date);
                 }
             }
         }
         return mList;
     }

     /**
      * A person knows the birthday if they have exactly one possible date
      *
      * @return
      */
     private boolean know(List<String> mList) {
         return mList.size() == 1;
     }

     /**
      * 获取data中的“月”的数据
      *
      * @param data
      *            getMonth("May 15")
      * @return May
      */
     private String getMonth(String date) {
         return date.split(" ")[0];
     }

     /**
      * 获取data中的“日”的数据
      *
      * @param data
      *            getMonth("May 15")
      * @return 15
      */
     private String getDay(String date) {
         return date.split(" ")[1];
     }

     public static void main(String[] args) {
         WhenIsCherylsBirthday whenIsCherylsBirthday = new WhenIsCherylsBirthday();

         System.out.println(whenIsCherylsBirthday.getCherylsBirthday(DATES));
     }
 }

顺着原文中的思路和Python代码修改的...话说Python还真是叼炸天啊...all()和filter()这俩函数简直叼...膜拜之...

疑惑：还是不太明白statement3的用处。。