一道面试题引发的思考

背景是一道面试题
有5个人坐在一起，问第五个人多少岁？他说比第4个人大2岁。问第4个人岁数，他说比第3个人大2岁。问第三个人，又说比第2人大两岁。问第2个人，说比第一个人大两岁。最后问第一个人，他说是10岁。请问第五个人多大？
写出计算第五个人多大的，过程（java）

如果这个题目给一个小学生，他也能很快做出来。大学生就不用说了，总结一下规律，比如一个等差数列几行代码就能解决问题。但要是你实现后面试则说其中一个说他说错了，是大3岁，而打破这种规则，你又如何处理呢。

这里就不对上诉做法进行任何说明。仅针对该类问题做一些分析。看下面关系
5-->4-->3-->2-->1
是不是一个链表关系，这里我想到了用责任链实现，对于上诉问题变化也能完美扩展，或许这才是面试者的本意。

第二题，可用责任链：

    package com.shuidexiongdi.chain.age;  
      
    public interface IPerson {  
          
        int getAge();  
          
        void setNextPerson(IPerson nextPerson);  
          
        void setBiggerThanNextPersonAge(int biggerThanNextPersonAge);  
      
    }  

    package com.shuidexiongdi.chain.age;  
      
    import org.apache.log4j.Logger;  
      
    public abstract class Person implements IPerson {  
          
        private Logger logger = Logger.getLogger(Person.class);  
          
        private int biggerThanNextPersonAge;  
          
        private IPerson nextPerson;  
          
        private int myAge;  
      
        public final int getAge() {  
            initMyAge();  
            if(this.nextPerson != null) {  
                this.myAge = this.nextPerson.getAge() + this.biggerThanNextPersonAge;   
            }  
            logger.info(this.getClass().getName() + " my age is:" + this.myAge);  
            return this.myAge;  
        }  
      
        public void setNextPerson(IPerson nextPerson) {  
            this.nextPerson = nextPerson;  
        }  
          
        void initMyAge() {  
            this.myAge = telYouMyAge();  
        }  
          
        abstract int telYouMyAge();  
          
        public void setBiggerThanNextPersonAge(int biggerThanNextPersonAge) {  
            this.biggerThanNextPersonAge = biggerThanNextPersonAge;  
        }  
      
    }  

    package com.shuidexiongdi.chain.age;  
      
    public class PersonFifth extends Person {  
      
        @Override  
        int telYouMyAge() {  
            System.out.println("you guess...");  
            return 0;  
        }  
      
    }  

    package com.shuidexiongdi.chain.age;  
      
    public class PersonFourth extends Person {  
      
        @Override  
        int telYouMyAge() {  
            System.out.println("you guess...");  
            return 0;  
        }  
      
    }  

    package com.shuidexiongdi.chain.age;  
      
    public class PersonThird extends Person {  
      
        @Override  
        int telYouMyAge() {  
            System.out.println("you guess...");  
            return 0;  
        }  
      
    }  

    package com.shuidexiongdi.chain.age;  
      
    public class PersonSecond extends Person {  
      
        @Override  
        int telYouMyAge() {  
            System.out.println("you guess...");  
            return 0;  
        }  
      
    }  

    package com.shuidexiongdi.chain.age;  
      
    public class PersonFirst extends Person {  
      
        @Override  
        int telYouMyAge() {  
            System.out.println("ok,I tell you! ");  
            return 10;  
        }  
      
    }  

    package com.shuidexiongdi.chain.age;  
      
    public class Client {  
          
        public static void main(String[] args) {  
            IPerson person5 = new PersonFifth();  
            IPerson person4 = new PersonFourth();  
            IPerson person3 = new PersonThird();  
            IPerson person2 = new PersonSecond();  
            IPerson person1 = new PersonFirst();  
              
            person5.setNextPerson(person4);  
            person5.setBiggerThanNextPersonAge(2);  
              
              
            person4.setNextPerson(person3);  
            person4.setBiggerThanNextPersonAge(2);  
              
            person3.setNextPerson(person2);  
            person3.setBiggerThanNextPersonAge(2);  
              
            person2.setNextPerson(person1);  
            person2.setBiggerThanNextPersonAge(2);  
              
            person1.setNextPerson(null);  
              
            person5.getAge();  
              
        }  
      
    }  

输出结果：
you guess...
you guess...
you guess...
you guess...
ok,I tell you!
2011-08-05 10:10:27  INFO Person[getAge]:21 - com.shuidexiongdi.chain.age.PersonFirstmy age is:10
2011-08-05 10:10:27  INFO Person[getAge]:21 - com.shuidexiongdi.chain.age.PersonSecondmy age is:12
2011-08-05 10:10:27  INFO Person[getAge]:21 - com.shuidexiongdi.chain.age.PersonThirdmy age is:14
2011-08-05 10:10:27  INFO Person[getAge]:21 - com.shuidexiongdi.chain.age.PersonFourthmy age is:16
2011-08-05 10:10:27  INFO Person[getAge]:21 - com.shuidexiongdi.chain.age.PersonFifthmy age is:18

评论

1 楼 envy2002 2012-02-03  

设 年龄分别为a,b,c,d,e

列出方程：a=b+2;
               b=c+2;
               .....

      用矩阵的方式解， 也可以啊。