1、斐波那契数列

package com.homework;
import java.util.Scanner;
public class Fibonacci{
    public static void main(String[] args) {
        System.out.println("请输入你想打印的项数：");
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] fib = new int[n];
        System.out.println("打印为：");
        fib[0] =1;
        fib[1] = 1;
        System.out.println(fib[0]);
        System.out.println(fib[1]);
        for(int i = 2;i < fib.length;i++){
            fib[i] = fib[i-1] + fib[i-2];
            System.out.println(fib[i]);
        }
    }
}

package Test1;
import java.util.Scanner;
public class Fib {//斐波那契数列
    public static void main(String args[]){
        int n;
        System.out.println("请输入你想打印的项数：");
        Scanner sc = new Scanner(System.in);
        n = sc.nextInt();
        int a = 1;
        int b = 1;
        System.out.println("打印的斐波那契数列为：");
        for(int i = 1;i <= n;i++){
            System.out.println(a);
            System.out.println(b);
            a = a+b;
            b = a+b;
        }
    }
}

2、字符串反转，单词内部字母顺序不变

package com.homework;
//单词反转,单词内字母顺序不变
public class swapString{
    public static void main(String[] args) {
        String str = "I am a student";
        String[] arr = str.split(" ");
        for(int i = 0;i < arr.length / 2;i++){
            String temp = arr[i];
            arr[i] = arr[arr.length -1 - i];
            arr[arr.length - 1 - i] = temp;
        }
        System.out.println("反转结果输出为：");
        for(int i = 0;i < arr.length;i++){
            System.out.print(arr[i]+" ");
        }
    }

3、1~n个数字中，1出现的次数

package com.homework;
//1~n的数字中1出现的次数
import java.util.Scanner;
public class NumOf1{
    public static void main(String[] args) {
        System.out.println("请输入：");
        Scanner sc = new Scanner(System.in);
        int num = sc.nextInt();
        int count = 0;
        for(int i = 1;i <= num;i++){
            int temp = i;
            while(temp != 0){
                if(temp % 10 == 1){
                    count++;
                }
                temp /= 10;
            }
        }
        System.out.println("其中1出现的次数为：");
        System.out.println(count);
    }
}

4、输入字符串打印出数字

package com.homework;

import java.util.Scanner;
public class StrToNum{
    private static int getBit(char[] arr) {
        return arr.length;
    }
    public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    String str = sc.next();
    char[] arr = str.toCharArray();
    int bit = getBit(arr);
    int result = 0;
    int flag = 1;
    for(int i = 0;i < arr.length;i++){
        if(arr[i] == '-'){
            flag *= -1;
        }else if(arr[i] == '+' || arr[i] == ' '){
            continue;
        }else{
            int n = arr[i] - ' ';
            result += (int)(n*Math.pow(10,--bit));
        }
        }
        result = result*flag;
    System.out.println(result);
    }
}

5、从一副扑克中随机抽取五张，判断是否为顺子

package com.homework;

import java.util.Random;
import java.util.Arrays;
import java.util.Scanner;

public class isContinuous{
    private static int getCountZero(int[] arr){
        int countZero = 0;
        for(int i=0;i<arr.length && arr[i] == 0;i++){
            countZero++;
            if(arr[i] == 0){
                countZero++;
            }
        }
        if(countZero>2){//重新随机
            isSeries();
//            return false;
        }
        return countZero;
    }
    private static boolean isSeries(int[] arr){
        Arrays.sort(arr);
        //1.大小王个数
        int countZero = getCountZero(arr);

        //2.统计间隔数
        int countGrap = 0;
        for (int i = countZero;i<arr.length-1;i++){
            if(arr[i] == arr[i+1]){
                return false;
            }
            if(arr[i]+1 != arr[i+1]){
                //统计间隔数  0 0 1 2 3 4 9
                for(int j=arr[i];j<arr[i+1]-1;j++){
                    //
                    countGrap++;
                }
            }
        }
        if(countZero >= countGrap){
            return true;
        }
        return false;
    }
    public static void isSeries(){
        Random random = new Random();
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入牌个数");
        int count = scanner.nextInt();
        int[] arr = new int[count];
        for(int i=0;i<arr.length;i++){
            arr[i] = random.nextInt(14);//[0,14)
        }

        System.out.println(Arrays.toString(arr));
        boolean flag = isSeries(arr);
        if(flag){
            System.out.println("是顺子");
        }else{
            System.out.println("不是顺子");
        }
    }
}

6、输入一个矩阵，从外到内顺时针打印输出

package com.homework;
//输入一个矩阵，从外到内以顺时针方向打印输出
public class printMatrix {
    public static void main(String[] args) {
        int[][] arr = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}, {13, 14, 15, 16}};
        //圈数，最外圈假设是0
        for (int j = 0; j < arr[0].length; j++) {
            //上
            for (int i = 0 + j; i < arr.length - j; i++) {//i表示列
                System.out.print(arr[0 + j][i] + "   ");
            }
            //右
            for (int i = 1 + j; i < arr.length - j; i++) {//i表示行
                System.out.print(arr[i][arr.length - 1 -j] + "   ");
            }
            //下
            for (int i = arr.length - 1 - 1 - j; i >= 0 + j; i--) {//i表示列
                System.out.print(arr[arr.length - 1 - j][i] + "   ");
            }
            //左
            for (int i = arr.length - 1 - 1 - j; i >= 1 + j; i--) {//i表示行
                System.out.print(arr[i][0 + j] + "   ");
            }
        }
    }
}

7、求1/1+1/2+1/3+…的值

import java.util.Scanner;
//求1/1+1/2-1/3+1/4.....的和
public class getSum {
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入：");
        int n = scanner.nextInt();
        double sum = 0;
        int flag = 1;
        for(int i = 1;i < n;i++){
            sum = sum + (1.0/i)*flag;
            flag *= -1;
        }
        System.out.println(sum);
    }
}

8、输入一个数判断是否为素数

import java.util.Scanner;

public class Test1 {
    public static void main(String[] args){

        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入：");
        int num = scanner.nextInt();

        if (num == 1 || num == 2){
            System.out.println(num + "是素数");
            return;
        }
        int i = 2;
        for(i = 2;i < num;i++){//变量的生命周期
            if(num % i == 0){
                System.out.println(num + "不是素数");
                break;
            }
            else{
                System.out.println(num + "是素数");
                break;
            }
        }

    }
}

import java.util.Scanner;

public class Test2 {

    public static boolean isPrime(int num) {
        if (num == 1 || num == 2) {
            return true;
        }
        int i = 0;
        for (i = 2; i < num; i++) {//变量的生命周期
            if (num % i != 0) {
                return true;
            } else {
                return false;
            }
        }
        return false;
    }
        public static void main(String[] args){
            Scanner scanner = new Scanner(System.in);
            System.out.println("请输入：");
            int num = scanner.nextInt();
            boolean flag = isPrime(num);
            if (flag = true) {
                System.out.println(num + "是素数");
            } else{
                System.out.println(num + "不是素数");
            }
        }
   }

9、输入一个数字，输出它的位数

import java.util.Scanner;

public class getBit {
    public static int getBit(int num){
        int count = 0;
        while(num != 0){
            num = num/10;
            count++;
        }
        return count;
    }
    public static void getEveryBitNumber(int num){
        int Bit = getBit(num);
        int count = 1;
        for(int i = 0;i < Bit;i++){
            count = count * 10;
            for(count = 1;count > 0;count = count/10){
                System.out.println(num/count);
                num = num % count;
            }
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一个数字：");
        int num = scanner.nextInt();
        int count = getBit(num);
        System.out.println(count);
    }
}

10、猜价格的小游戏代码

import java.util.Random;
import java.util.Scanner;

public class Price {
    public static void main(String[] args) {
        while (true) {
            Random random = new Random();
            int goodsPrice = random.nextInt(1000) + 1;
            System.out.println("请输入你猜的价格：");
            //计数器
            int count = 0;
            Scanner scanner = new Scanner(System.in);
            //猜价格，三次机会
            while (count < 3) {
                count++;
                int guessPrice = scanner.nextInt();
                    if (guessPrice > goodsPrice) {
                        System.out.println("你猜贵了呢！");
                    } else if (guessPrice < goodsPrice) {
                        System.out.println("你猜少了哦！");
                    } else {
                        System.out.println("恭喜你，猜对啦！");
                        break;
                    }
                }
                System.out.println("请选择是否重新猜价格：  1.是   2.否");
                //处理方法二，比较字符串
                String selectSwitch = scanner.next();
                if (selectSwitch.equals("是")){
                    continue;
                }if (selectSwitch.equals("否")){
                    break;
                }
//                处理方式1，数字1代表继续2代表返回
              int selectSwitchNumber = scanner.nextInt();
                if (selectSwitchNumber == 1) {
                    continue;
                }
                else if(selectSwitchNumber == 2){
                    break;
                }
            }
        }
    }

11、使用integer的静态方法parseInt将字符串转变为制指定进制的数字

public class Test2 {
    public static void main(String args[]){
        String s = "-123";//定义字符串
        int b = Integer.parseInt(s,10);//使用integer的静态方法parseInt将字符串转变为制指定进制的数字
        System.out.println(b);//输出
        }
    }