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Java经典逻辑编程三

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求1+2!+3!+…+20!的和

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import java.util.Scanner;
public class class_name {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
         
        System.out.println("你想计算到哪个数的阶乘的和");
        int num = in.nextInt();
         
        long temp = 0L;
        long sum = 0L;
        for(int i = 1; i <= num; i++){
            temp = recursion(i);
            sum += temp;
        }
        System.out.println("计算到" + num + "的阶乘和是 " + sum);
    }
 
            //计算某个数 num 的阶乘
    private static long recursion(int num) {
        // TODO Auto-generated method stub
        if(num > 1){
            return num * recursion(num - 1);
        }
        return 1;
    }
}

给一个不多于5位的正整数，要求: 一、求它是几位数；二、逆序打印出各位数字

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import java.util.Scanner;
public class class_name {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
         
        System.out.println("请输入一个不多于5位的整数");
        int num = in.nextInt();
         
        int n = 1;
        System.out.print("这个数的逆序为：");
        while(num / 10 > 0){
            n++;
            int tmp = num % 10;
            System.out.print(tmp);
            num /= 10;
        }
        System.out.println(num);
        System.out.println("这个数共有" + n + "位数");
    }
}

请输入星期几的第一个字母来判断以下是星期几，如果第一个字母一样，则继续判断第二个字符。

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import java.util.Scanner;
public class class_name {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
         
        char firstletter, secondletter;     //存放第一第二个字母
        System.out.println("请输入第一字母");
        String letter = in.next();
         
        firstletter = letter.charAt(0);
        switch(firstletter){
        case 'm':
        case 'M': 
            System.out.println("是星期一");break;
        case 'w':
        case 'W':
            System.out.println("是星期三");break;
        case 'f':
        case 'F':
            System.out.println("是星期五");break;
        case 't':
        case 'T':
            System.out.println("仅由该字母无法判断出星期几，请输入第二个字母");
            letter = in.next();
            secondletter = letter.charAt(0);
            if(secondletter == 'u' || secondletter == 'U'){
                System.out.println("是星期二");
                break;
            }else if(secondletter == 'h' || secondletter == 'H'){
                System.out.println("是星期四");
                break;
            }else{
                System.out.println("输入错误");
            }
        case 's':
        case 'S':
            System.out.println("仅由该字母无法判断出星期几，请输入第二个字母");
            letter = in.next();
            secondletter = letter.charAt(0);
            if(secondletter == 'a' || secondletter == 'A'){
                System.out.println("是星期六");
                break;
            }else if(secondletter == 'u' || secondletter == 'U'){
                System.out.println("是星期天");
                break;
            }else{
                System.out.println("输入错误");
            }
        }
    }
}

求一个3*3矩阵对角线元素之和

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import java.util.Scanner;
public class class_name {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
         
        //输入数据
        int[][] mat = new int[3][3];
        for(int i = 1; i <= 3; i++){
            for(int j = 1; j <= 3; j++){
                System.out.println("请输入第" + i + "行第" + j + "列的整数");
                mat[i -1][j - 1] = in.nextInt();
            }
        }
         
        //显示数据
        for(int i = 0; i < 3; i++){
            for(int j = 0; j < 3; j++)
                System.out.printf("%d\t",mat[i][j]);    // \t是制表符
        System.out.println();
        }
         
        //计算对角线元素和
        //从左上至右下的数归为主对角线，从左下至右上的数归为副对角线。
        int sum1 = mat[0][0] + mat[1][1] + mat[2][2];
        int sum2 = mat[2][0] + mat[1][1] + mat[0][2];
        System.out.println("主对角线上元素和为 " + sum1);
        System.out.println("副对角线上元素和为 " + sum2);
    }
}

有一个已经排好序的数组。现输入一个数，要求按原来的规律将它插入数组中。

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import java.util.Scanner;
public class class_name {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
         
        int[] ary = {10, 15, 20, 25, 30, 35, 40, 45, 50};
        int[] changedAry = new int[ary.length + 1];
         
        System.out.print("初始数组：");
        for(int i = 0; i < ary.length; i++){
            changedAry[i] = ary[i];
            System.out.print(ary[i] + " ");
        }
        System.out.println();
         
        System.out.println("请输入一个整数");
        int num = in.nextInt();
         
        System.out.print("插入数字后的数组：");
        insort(changedAry, num);
    }
 
    private static void insort(int[] changedAry, int num) {
        // TODO Auto-generated method stub
        for(int i = 0; i < changedAry.length; i++){
            if(num < changedAry[i]){         //找到插入位置
                for(int j = changedAry.length - 1; j > i;j--){
                    changedAry[j] = changedAry[j - 1];  //待插入位置及以后的数后退一个位置
                }
                changedAry[i] = num;
                break;
            }
        }
        if(num > changedAry[changedAry.length - 1])      //待插入数大于所有数
            changedAry[changedAry.length - 1] = num;
         
        for(int k = 0; k < changedAry.length; k++)
            System.out.print(changedAry[k] + " ");
    }
}

将一个数组逆序输出

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public class class_name {
    public static void main(String[] args) {
        //这里直接初始化一个数组
        int[] ary = {1, 2, 3, 4, 5, 6, 7, 8, 9};
//      String[] ary = {"i", "love", "you"};        //字符（串）数组也可以
         
        System.out.print("数组初始顺序为：");
        for(int i = 0; i < ary.length; i++)
            System.out.print(ary[i] + " ");
        System.out.println();       //换行
         
        System.out.print("数组的逆序为：");
        for(int i = ary.length - 1; i >= 0; i--)
            System.out.print(ary[i] + " ");
        System.out.println();
    }
}

取一个整数a从右端开始的4~7位。

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import java.util.Scanner;
public class class_name {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.println("请输入一个大于等于 7 位的整数");
        long sum = in.nextLong();
        Long sum1 = new Long(sum);      //Long是 long 的包装类
        String sum2 = sum1.toString();
        System.out.println(sum2.substring(sum2.length() - 7, sum2.length() - 3));
    }       // substring 截取两参数间的字符串
}

打印出杨辉三角形

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public class class_name {
    public static void main(String[] args) {
        int i, j;
        int[][] num = new int[10][10];
        for (i = 0; i < 10; i++) {// 把所有的 1 放入数组
            num[i][0] = 1;
            num[i][i] = 1;
        }
 
        for (i = 2; i < 10; i++) {// 计算数组的其他数
            for (j = 1; j < i; j++) {
                num[i][j] = num[i - 1][j - 1] + num[i - 1][j];
            }
        }
 
        for (i = 0; i < 10; i++) { 
                        // k < 4 倍的空格是因为输出每个数字时用了 4 个占位符
            for (int k = 0; k < 4 * (10 - i) / 2; k++)       // 输出空格
                System.out.printf(" ");
 
            for (j = 0; j <= i; j++) {
                System.out.printf("%4d", num[i][j]); // 每个数字 4 个占位符
            }
            System.out.println();
        }
    }
}

输入数组，最大的与第一个元素交换，最小的与最后一个元素交换，输出数组。

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import java.util.Scanner;
public class class_name {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
         
        System.out.println("请输入数组长度");
        int arylen = in.nextInt();
        int[] num = new int[arylen];
         
        for(int i = 0; i < num.length; i++) {
            System.out.printf("请输入第 %d 个数：", i + 1);
            num[i] = in.nextInt();
        }
         
        System.out.println("变化前的数组：");
        outArray(num);
            //循环找出最大值、最小值
        int max = num[0];
        int min = num[0];
        for(int i = 1; i < num.length; i++) {
            if(num[i] > max)
                max = num[i];
            if(num[i] < min)
                min = num[i];
        }
                //替换
        num[0] = max;
        num[num.length - 1] = min;
         
        System.out.println("变化后的数组：");
        outArray(num);
    }
 
    private static void outArray(int[] num) {
        // TODO Auto-generated method stub
        for(int i = 0; i < num.length; i++)
            System.out.print(num[i] + " ");
        System.out.println();
    }
}

有n个整数，使其前面各数顺序向后移m个位置，最后m个数变成最前面的m个数。

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import java.util.Scanner;
public class class_name {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int[] num = {14, 32, 5, 42, 36, 80};
        int[] temp = new int[num.length];
         
        System.out.println("移动前的数组：");
        for(int i = 0; i < num.length; i++){
            temp[i] = num[i];
            System.out.print(num[i] + " ");
        }
        System.out.println();
         
        System.out.println("需要向后移动几个位置");
        int m = in.nextInt();
         
        for(int i = 0; i < num.length; i++){
            int t = (i + m) % num.length;
            num[t] = temp[i];       //这行的 t 和 i 互换一下就变成了（1）
        }
         
        System.out.println("移动后的数组：");
        for(int i: num)
            System.out.print(i + " ");
        System.out.println();
    }
}
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