经典的农夫养牛问题（常考的面试题）

int[] cows= new int[20];

cows[0]=cows[1]=cows[2]=1;

cows[3]=2;

for (int i = 4; i < cows.length; i++) {

	cows[i]=cows[i-4]+cows[i-3]+cows[i-2];

}

for (int i = 0; i < cows.length; i++) {

	System.out.print(cows[i]+" ");

}

//55把我误导了 看来还是我是正确的

    /**

     * 一个农夫养了一头牛，三年后，这头牛每年会生出1头牛，生出来的牛三年后，又可以每年生出一头牛……问农夫10年后有多少头牛?n年呢？（用JAVA实现）

     * 首先鄙视一下牛不死现象和公牛产子现象

     * @param str

     */

    public static void main(String[] str)

    {

        

       System.out.println(process(1,10));

        

    }

    

    public static int process(int initCount,int year)

    {

        int zeroYearsOld = initCount;       //刚出生的牛 初始化为1

        int oneYearsOld = 0;                //1岁的 数量

        int towYearsOld = 0;                //2岁的数量

        int ripeCount = 0;                  //成熟的,可以无性繁殖的数量

        int max = initCount;                //总数

        

        for(int i=0;i<year;i++)

        {

            int temp = towYearsOld;         //今年牛成熟的数量

            towYearsOld = oneYearsOld;      //牛长大一岁

            oneYearsOld = zeroYearsOld;     //牛长大一岁

            ripeCount += temp;              //成熟数量加上今年成熟的

            max +=ripeCount;                //所有成熟的牛都会生一个,所以原来牛群数量加上成熟牛的数量等于现在数量

            zeroYearsOld = ripeCount;       //刚出生的牛

            

            System.out.println("第"+(i+1)+"年:牛的数量为"+max+"头，新增"+zeroYearsOld+"头");

        }

        

        return max;

    }

import java.util.Scanner;





/**

 * 

 * @author crose_1988@163.com 

 */

public class Cows {

	private static void forEachYear(int[] waitYears) {

		int[] cows = waitYears.clone();

		

		waitYears[cows.length-1] = cows[0];

		waitYears[0] = cows[0] + cows[1];

		

		for (int i=cows.length-2; i>0; i--)

			waitYears[i] = cows[i+1];

	}

	

	public static void main(String[] args) {

		int waitYears[] = {0, 0, 1};

		System.out.print("input years: ");

		Scanner scanner = new Scanner(System.in);

		

		try {

			int year = scanner.nextInt();

			int counts = 0;

			

			for (int i=1; i<=year; i++)

				forEachYear(waitYears);

			for (int i=0; i<waitYears.length; i++)

				counts += waitYears[i];

			System.out.println("cows: " + counts);

		} catch (Exception e) {

			e.printStackTrace();

		}

	}

}

package org.lkm.test;



import java.util.ArrayList;

import java.util.List;



/**

 * @author 

 */

public class c {



	private int age = 0;



	/**

	 * 是否可以生产小牛

	 * 

	 * @return True | False

	 */

	public boolean isCreatSmallCow() {

		return (age >= 3) ? true : false;

	}



	/**

	 * 过年了，年龄又大了一岁

	 */

	public void addYear() {

		age++;

	}



	/**

	 * @param args

	 */

	public static void main(String[] args) {

		List<c> cowList = new ArrayList<c>();

		// 第一头小牛

		cowList.add(new c());

		int yearCount = 10;

		// 就这样一年年过

		for (int i = 1; i <= yearCount; i++) {

			int rowNum = cowList.size();

			for (int j = 0; j < rowNum; j++) {

				c o = cowList.get(j);

				// 过年了

				o.addYear();

				// 能生小牛吗？

				if (o.isCreatSmallCow()) {

					cowList.add(new c());

				}

			}

		}

		System.out.println(yearCount + "年后将有【" + cowList.size() + "】头牛。");

	}

}