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。。