【Java】算法题

public class mission1 {//      伟大的马克思的手稿中有这样一道有趣的数学题：//       有30个人，其中可能有男人，女人，小孩。他们在一家饭馆中吃饭，共花费50先令。//       如果每个男人吃饭要花3先令，每个女人要花2先令，每个小孩要花1先令，//       问男人，女人，小孩各多少人？(有几种可能性)    public static void main(String[] args) {                int nman = 0;        int nwoman = 0;        int nboy = 0;        int count = 0;                System.out.println("男人\t" + "女人\t" + "小孩");        //        for (nman = 0; nman<17; nman++) {//            //            for(nwoman = 0; nwoman<=25; nwoman++){//                //                for(nboy = 0; nboy<=50; nboy++){//                    //                    if((50 == (nman*3 + nwoman*2 + nboy*1))&&(30 == nman + nwoman + nboy)){//                        System.out.println(nman + "\t" + nwoman + "\t" + nboy);//                        count++;//                    }//                }//            }//        }        for(; nman <= 10; nman++){            //nman + nwoman + nboy = 30            //nman*3 + nwoman*2 + nboy*1 = 50                        nwoman = 20 - 2 * nman;            nboy = 30 - nman - nwoman;                        if(50 == (nman*3 + nwoman*2 + nboy*1)){                System.out.println(nman + "\t" + nwoman + "\t" + nboy);                count++;            }        }        System.out.println("总共有" + count + "种。");    }}

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//    1. 两数交换程序 (两种方法)////    输出互换前手中的纸牌：//    左手中的纸牌： 10//    右手中的纸牌： 8////    输出互换后手中的纸牌：//    左手中的纸牌： 8//    右手中的纸牌： 10//   提示： 可以设置一个中间数public class mission1 {    public static void main(String[] args) {        int a = 10;        int b = 8;        System.out.println("\t交换前：a = " + a + "\tb = " + b);        method1 m1 = new method1(a, b);        method2 m2 = new method2(a, b);        method3 m3 = new method3(a, b);    }}class method1 {    int temp;    public method1(int a, int b) {        temp = a;        a = b;        b = temp;        System.out.println("method1  交换后：a = " + a + "\tb = " + b);    }}class method2 {    public method2(int a, int b) {        a = a ^ b;        b = a ^ b;        a = a ^ b;        System.out.println("method2  交换后：a = " + a + "\tb = " + b);    }}class method3 {    public method3(int a, int b) {        a = a + b;        b = a - b;        a = a - b;        System.out.println("method3  交换后：a = " + a + "\tb = " + b);    }}

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import java.util.Scanner;public class mission2 {//    求2+22+222+2222+22222+.....n次 的值//    提示：//         System.out.println("请输入统计的次数：");//            int n = input.nextInt();    public static void main(String[] args) {                Scanner sc = new Scanner(System.in);        Integer num = sc.nextInt();                int factor = 0;        int sum = 0;        int count = 0;        //        for (int j = num; j >=1; j--) {//            //            for(int i = j - 1; i >= 0; i--){//                //                sum += factor * Math.pow(10, i);//                //            }//            count++;//        }        for (int i = 0; i < num; i++) {            factor = factor * 10 + 2;            sum += factor;            count++;        }//        System.out.println(factor);                System.out.println("统计" + count + "次。");        System.out.println("值为： " + sum);    }}

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public class Daffodil {//     打印出所有的 "水仙花数 "，所谓 "水仙花数 "是指一个三位数，//      其各位数字立方和等于该数本身。例如：153是一个 "水仙花数 "，//      因为153=1的三次方＋5的三次方＋3的三次方        public static void main(String[] args) {                Daffodil da = new Daffodil();                for(int i = 100; i<=999; i++){                        int a = i / 100;            int b = i / 10 % 10;            int c = i % 10;                        if(da.isDaffodil(i)){                                System.out.println(i + "=" + a + "的三次方 + " +                        b + "的三次方 + " + c + "的三次方");            }        }    }        public boolean isDaffodil(int i){                int a = i / 100;        int b = i / 10 % 10;        int c = i % 10;                if (i == (a*a*a + b*b*b + c*c*c)) {            return true;        } else{            return false;        }    }    }

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//求1+2!+3!+...+20!的和public class mission2 {    public static void main(String[] args) {                int sum = 0;                for (int i = 1; i <= 20; i++) {            sum += multi(i);        }        System.out.println(sum);    }        public static int multi(int num){ //计算阶乘                if(num == 1 || num == 0){            return 1;        } else{            return (num * multi(--num));        }            }}