package com.mh.basic.one;

public class Recursion {

    
    public static int f(int i){
        if( i == 1  || i == 2 ){
            return 1;
        }
        
        else{
            return f(i-1) + f(i-2);
        }
    }
    
    public static void main(String[] args) {
        
        System.out.println(Recursion.f(20));
    }
    
    
    
}

package com.mh.basic.one;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
//创建一个兔子类
public class Rabbit {

    private int age ;//有一个属性age,用来记录年龄(按月计算)
    
    private static List<Rabbit> list = new ArrayList<Rabbit>(Arrays.asList(new Rabbit(1)));//定义一个"兔子窝",兔子窝中本来就有一对兔子
    
    public Rabbit(int age){//构造方法
        this.age = age;
    } 
    
    public static Rabbit birth(){//兔子有生小兔子的行为
        return new Rabbit(1);
    }
    

    public static int getSize(List<Rabbit> list){//获得兔子窝中的兔子总量
        return list.size();
    }
    
    
    public static int countRabbits(int month){//计算给定月份兔子窝中应有多少兔子
        
        if( month == 1 || month == 2) {
            
            return 1;
            
        }else{
                list.get(0).age = 3;
            }
            
        
        Rabbit curr_Rabbit = null;
        
        for(int i = 3 ; i <= month ; i++){//从三月份开始
            
            for(int j = 0; j < list.size(); j++){
                
                curr_Rabbit = list.get(j);
                
                if(curr_Rabbit.age >= 3){//如果年龄大于等于三个月,可以生兔子
                    
                    list.add(birth());
                }
                
                curr_Rabbit.age++;//不然年龄加1
            }
        }
        return getSize(list);
    }

    
    public static void main(String[] args) {
        System.out.println(Rabbit.countRabbits(20));
    }
}