Java的算法题

 /** *//**父子俩的年龄：父亲今年30岁，儿子今年6岁，问多少年后父亲的年龄是儿子年龄的2倍。*/
package exec;

public class Age {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int father = 30;
        int son = 6;
        for(int i=1;i<100;i++)
        {
            if((father+i)==((son+i)*2)){
                System.out.println(i + " 年");
            }
        }
    }
}

 

/** *//**编写程序,将两个各有6个整数的数组,合并成一个由小到大排列的数组,(该数组的长度为12)*/
package exec;

import java.util.Arrays;

public class Arrary {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int a[] = { 1, 3, 5, 8, 9, 4 };
        int b[] = { 2, 4, 7, 6, 5, 9 };
        int c[] = new int[12];
        for (int i = 0; i < 6; i++) {
            c[i] = a[i];
            c[i + 6] = b[i];
        }
        Arrays.sort(c);
        for (int i = 0; i < 12; i++) {
            System.out.print(c[i] + " ");
        }
    }

}

 

/** *//** 一个球从100米高度自由落下后，反弹回原来高度的一半。按此规律，到第10次落地时，行程共有多少米？
 * 然后将反弹起多高？ */
package exec;

public class BallFall {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        float heigher = 100;
        float sum = 0;
        for (int i = 1; i < 10; i++) {
            heigher /= 2;
            sum += heigher;
            System.out.println("第" + i + "次" + "总行程" + sum + "米" + "反弹"
                    + heigher + "米");
        }

    }

}

 

/** *//** 换硬币：把一元人民币换成5分、2分、1分的硬币，有多少种换法? */
package exec;

public class ChangeCoin {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int num = 0;

        for (int i = 1; i <= 20; i++) {
            for (int j = 1; j <= 50; j++) {
                for (int k = 1; k <= 100; k++) {
                    if (5 * i + 2 * j + 1 * k == 100) {
                        num += 1;
                    }
                }
            }
        }
        System.out.print(num + "种换法");
    }
}

 

/** *//**牛的繁殖问题 ：有位科学家曾出了这样一道数学题：有一头母牛，它每年年初要生一头小母牛；
 * 每头小母牛从第四个年头起，每年年初也要生一头小母牛。按此规律，若无牛死亡，第20年头上共有多少头母牛？*/
package exec;

public class CountCow {
    int[] cowNumber = new int[21];

    public void count(int increaseCycle, int years) {
        cowNumber[0] = 1;
        for (int currentYear = 1; currentYear <= years; currentYear++) {
            if (currentYear < increaseCycle) {
                cowNumber[currentYear] = cowNumber[currentYear - 1] + 1;
            } else {
                cowNumber[currentYear] = cowNumber[currentYear - 1]
                        + cowNumber[currentYear - increaseCycle + 1];

            }
            System.out
                    .println("第" + currentYear + "年" + cowNumber[currentYear]);
        }
    }

    public static void main(String[] args) {
        int increaseCycle = 4;
        int years = 20;

        CountCow cow = new CountCow();
        cow.count(increaseCycle, years);
    }
}

 

/** *//** 打印出500之内所有能被7或9整除的数*/
package exec;

public class Divide {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        for (int i = 0; i <= 500; i++) {
            if ((i % 7 == 0) | (i % 9 == 0)) {
                System.out.print(i + " ");
            }
        }
    }

}

 

/** *//**
 * 编写一个Java程序 使它随即产生1800到2000之间的年份,打印它是否是一个闰年,闰年是1584年以后的年份,它要能被400整除,
 
 * 要能被4整除但是不能被100整除,已知使用Math.random()方法可以产生0到1之间的随即小数. )

 */
package exec;

public class EmergerYear {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        for (int i = 0; i < 100; i++) {
            long year = (Math.round(Math.random() * 200) + 1800);
            if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
                System.out.println(year + "是闰年!");
            } else
                System.out.println(year + "不是闰年!");
        }
    }

}

 

/** *//**编写程序以递归的方式实现1+2+3++n(n=200)的计算.*/
package exec;

public class Number {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        System.out.print(numbers(200));
    }
    public static int numbers(int n){
        return n<=1?1:n+numbers(n-1);
    }
}

 

/** *//** 给定一个数，并由键盘输入若干个数，找出与预先给定的数最接近的数，
 * 并指出它是由键盘输入的第几个数。
 */
package exec;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class NumberCompare {
    public static final int NUMBER = 80; // 给定一个要比较的数

    public static void main(String args[]) {
        System.out.print("Please input numbers: ");
        BufferedReader io = new BufferedReader(new InputStreamReader(System.in));
        try {
            // 从键盘输入若干数
            String line = io.readLine();
            // 放入数组中
            String[] items = line.split(" ");
            int temp = 5000, x = 0, place = 0;
            System.out.println("target number: 80");
            // 和给定的数比较大小
            for (int i = 0; i < items.length; i++) {
                if (Integer.parseInt(items[i]) > NUMBER) {
                    x = Integer.parseInt(items[i]) - NUMBER;
                } else {
                    x = NUMBER - Integer.parseInt(items[i]);
                }
                if (x < temp) {
                    temp = x;
                    place = Integer.parseInt(items[i]);
                }
            }
            System.out.println("place: " + place);
            io.close();
            System.exit(0);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
 

/** *//**使用Java,long.Math类,生成10个0到99之间的随即整数,求出它们中的最小值和最大值*/
package exec;

import java.util.Iterator;
import java.util.TreeSet;

public class RandomNumber {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        /** *//**方法1
        long max = 50;
        long min = 50;
        for(int i=0; i<10; i++){
            long number = Math.round(Math.random()*99 + 1);
            System.out.print(number + " ");
            max = Math.max(max, number);
            min = Math.min(min, number);
            if(i == 9){
                System.out.print(" Math MaxNumber=" + max + " MinNumber=" + min);
            }
        }
        */
        //方法2
        TreeSet ts = new TreeSet();
        for(int i=0; i<10; i++){
            long number = Math.round(Math.random()*99 + 1);
            System.out.print(number + " ");
            ts.add(number);
        }
        System.out.println();
        Iterator it = ts.iterator();
        while(it.hasNext()){
            System.out.print(it.next() + " ");
           
        }
        System.out.print(" Math MaxNumber=" + ts.last() + " MinNumber=" + ts.first());
    }
       
}

 

/** *//**假设有一条钢材长2000米,每天截取其中的一半,编写一程序求出多少天后,钢材的长度小于5米.*/
package exec;

public class SteelSection {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int i = 0;
        float steel = 2000f;
        while (steel >= 5) {
            i++;
            steel = steel / 2;
            System.out.println(i + "天后钢管长" + steel + "米");
        }
    }

}

 

/** *//**完全数是指其所有因子(包括1但不包括该数自身)的和等于该数,例如28=1+2++4+7+14,28就是一个完全数.
 * 编写一个程序求出2到10000之间的所有完全数.*/
package exec;

public class WanNumber {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int m = 0;
        for (int n = 2; n <= 10000; n++) {
            m = 0;
            for (int i = 1; i < n; i++) {
                if (n % i == 0) {
                    m += i;
                    if (m == n) {
                        System.out.println(n + "个完全数");
                    }
                }
            }
        }
    }

}

 

/**//*编写一个Java类Prime,其中只有一个静态方法. boolean.isPrin=me(int n)//方法测试n是否是素数,
 * 如果是返回true 否则返回false  已知Babbage函数发f（x)=x*x+x+41,其中x为自然数,
 * 当x小于特定的n之间所有的函数均为素数,编写一个测试类,其中的main方法找出这个特定n值.
 */

package exec;

public class Test {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        int num = 200000; // 表示1-num之间的自然数
        for (int i = 1; i <= num; i++) {
            if (Prime.me(i)) {
                System.out.println(i + "是素数");
            } else {
                System.out.println(i + "不是素数");
            }
        }

    }

}
package exec;

public class Prime {
    public static boolean me(int n) {
        for (int x = 1; x < n; x++) {
            if (n == x * x + x + 41) {
                return true;
            }
        }
        return false;
    }

}