Java编程实战-优快云博客

本文链接：https://blog.youkuaiyun.com/weixin_45091028/article/details/104329004


import java.util.Scanner;
class Demo04_01{
    public static void main(String[] args){
        //1.先输入一个数字
        Scanner scanner=new Scanner(System.in);
        System.out.print("请输入一个数字:");
        long num=scanner.nextLong();
        //2.调用函数将num拆分求和
        int sum=sumDigits(num);
        System.out.println(sum);
    }
    public static int sumDigits(long n){
        int sum=0;
        while(true){
            sum+=n%10;
            n/=10;
            if(n==0){
                return sum;
            }
        }
    }
}

import java.util.Scanner;
class Demo4_02{
    public static void main(String[] args){
        System.out.print("请输入一个整数:");
        Scanner input=new Scanner(System.in);
        int num=input.nextInt();
        System.out.println(num+" is "+isPalindrome(num));

    }
    public static int reverse(int number){
        int sum=0;
        for(int i=number;i!=0;){
            sum=sum*10+i%10;
            i/=10;
        }
        return sum;
    }
    public static boolean isPalindrome(int number){
         int num1=reverse(number);
         return num1==number?true:false;
    }
}


import java.util.Scanner;
class Demo4_03{
    public static void main(String[] args){
        System.out.print("请输入一个n:");
        Scanner input=new Scanner(System.in);
        int n=input.nextInt();
        displaypattren(n);
    }
    public static void displaypattren(int n){
        for(int i=1;i<=n;i++){
            for(int k=n-1;k>=i;k--){
                System.out.print("  ");
            }
            for(int j=i;j>=1;j--){
                System.out.print(j+" ");
            }
        System.out.println();
        }
    }
}

import java.util.Scanner;
class Demo4_05{
    public static void main(String[] args){
        System.out.print("请输入一个n: ");
        Scanner input=new Scanner(System.in);
        int n=input.nextInt();
        System.out.print(sqrt(n));
    }
    public static double sqrt(long n){
        double r;
        double last_guess = n;
	    double new_guess = n / 2;
	while ((last_guess-new_guess)/last_guess>0.01)
	{
		last_guess = new_guess;
		r = n / new_guess;
		new_guess = (new_guess + r) / 2;
        }
        return new_guess;
    }
}

class Demo4_06{
    public static void main(String[] args){
        int count=0;    //表示回文素数的个数
        int num=2;      //表示可能的回文素数的数字 从2开始~?
        while(true){
            //如果num是 回文素数
            if(isHuiWenAndSuShu(num)){
                count++;
                System.out.print(num+" ");
                if(count%10==0){
                    System.out.println();
                }
            }
            if(count==100){
                break;
            }
            num++;
        }
    }
    public static boolean isHuiWenAndSuShu(int num){
        return isHuiWen(num)&&isSuShu(num);
    }
    public static boolean isHuiWen(int num){
        return reverse(num)==num;
    }
    public static int reverse(int num){
        int sum=0;
        while(true){
            sum=sum*10+num%10;
            num/=10;
            if(num==0){
                return sum;
            }
        }
    }
    public static boolean isSuShu(int num){
        for(int i=2;i<=num/2;i++){
            if(num%i==0){
                return false;
            }
        }
        return true;
    }
}


class Demoo4_07{
    public static void main(String[] args){
        int count=0;
        int num=2;
        while(true){
            if(isFanZhuanSuShu(num)){
                count++;
                System.out.print(num+" ");
                if(count%10==0){
                    System.out.println();
                }
            }
            if(count==100){
                return; //结束当前函数
            }
            num++;
        }
    }
    //1.本身是素数
    //2.反转之后也是素数
    //3.不能是回文
    //素数()  反转() 回文功能()
    public static boolean isFanZhuanSuShu(int num){
        return isSuShu(num)&&isSuShu(reverse(num))&&!isHuiWen(num);
    }
    //回文功能
    public static boolean isHuiWen(int num){
        return reverse(num)==num;
    }
    //素数功能
    public static boolean isSuShu(int num){
        for(int i=2;i<=num/2;i++){
            if(num%i==0){
                return false;
            }
        }
        return true;
    }
    //反转功能
    public static int reverse(int num){
        int sum=0;
        while(true){
            sum=sum*10+num%10;
            num/=10;
            if(num==0){
                return sum;
            }
        }
    }
}

import java.util.Scanner;
class Demo04_04{
    public static void main(String[] args){
        //1.先提示用户输入密码(String password)
        Scanner scanner=new Scanner(System.in);
        System.out.print("请输入密码:");
        String password=scanner.nextLine();

        //2.将密码传入 boolean isValid(password)
        if(isValid(password)){
            System.out.println("密码合法!");
        }else{
            System.out.println("密码不合法!");
        }
    }
    //3.isValid()
    //3.1 长度 isLengthValid()
    //3.2 组成 isContentValid()
        //3.2.1 isLetter(c) 判断该字符是否为字母字符
        //3.2.2 isDigit(c) 判断该字符是否为数字字符
    //3.3 特殊至少俩数字 isNumberValid() isDigit(c)
    public static boolean isValid(String s){
        return isLengthValid(s)&&isContentValid(s)&&isNumberValid(s);
    }
    public static boolean isLengthValid(String s){
        return s.length()>=8;
    }
    public static boolean isContentValid(String s){
        char c=' ';
        for(int i=0;i<s.length();i++){
            c=s.charAt(i);
            if(!isLetter(c)&&!isDigit(c)){
                return false;
            }
        }
        return true;
    }
    public static boolean isNumberValid(String s){
        int count=0;
        char c=' ';
        for(int i=0;i<s.length();i++){
            c=s.charAt(i);
            if(isDigit(c)){
                count++;
            }
        }
        return count>=2;
    }
    // a~z A~Z 只需要比较ASCII值
    // 'a'<=c<='z' || 'A'<=c<='Z'
    // '0'<=c<='9'
    public static boolean isLetter(char c){
        return c>='a'&&c<='z' || c>='A'&&c<='Z';
    }
    public static boolean isDigit(char c){
        return c>='0'&&c<='9';
    }

}

class Demo04_08{
    public static void main(String[] args){
        String s="abcasjdjhsadadbhasdvasbd";
        System.out.println(count(s,'a'));
    }
    public static int count(String s,char c){
        int count=0;
        for(int i=0;i<s.length();i++){
            if(s.charAt(i)==c){
                count++;
            }
        }
        return count;
    }
}

class Demo04_09{
    public static void main(String[] args){
        String s="123456";
        System.out.println(reverse(s));
    }
    public static String reverse(String s){
        String res="";
        for(int i=s.length()-1;i>=0;i--){
            res+=s.charAt(i);
        }
        return res;
    }
}

class Demo04_10{
    public static void main(String[] args){
        String s="Welcome To China";
        System.out.println(getUpperCase(s));
    }
    public static int getUpperCase(String s){
        int count=0;
        for(int i=0;i<s.length();i++){
            if(isUpperCase(s.charAt(i))){
                count++;
            }
        }
        return count;
    }
    public static boolean isUpperCase(char c){
        return c>='A'&&c<='Z';
    }
}

class Demo04_11{
    public static void main(String[] args){
        String s1="Welcome";
        String s2="Welcome";
        System.out.println(getCommonPrefix(s1,s2));
    }
    public static String getCommonPrefix(String s1,String s2){
         第一种思路
        String minStr="";
        String maxStr="";
        if(s1.length()<=s2.length()){
            minStr=s1;
            maxStr=s2;
        }else{
            minStr=s2;
            maxStr=s1;
        }
        for(int i=0;i<minStr.length();i++){
            if(minStr.charAt(i)!=maxStr.charAt(i)){
                return minStr.substring(0,i);
            }
        }
        return minStr;
                第二种思路
        int pa=0;// s1的指针
        int pb=0;// s2的指针
        while(true){
            if(s1.charAt(pa)!=s2.charAt(pb)){
                return s1.substring(0,pa);
            }
            if(s1.charAt(pa)==s2.charAt(pb)){
                pa++;
                pb++;
            }
            if(pa==s1.length()){
                return s1;
            }
            if(pb==s2.length()){
                return s2;
            }
        }
    }
}

class Demo04_12{
    public static void main(String[] args){
        String s="AB8C";
        //A B 8 C
        //0 1 2 3
        //3 2 1 0
        System.out.println(hexToDeimal(s));
    }
    public static int hexToDeimal(String s){
        int num=0;
        char c=' ';
        for(int i=0;i<s.length();i++){
            c=s.charAt(s.length()-1-i);
            /*
            A=10 B=11 C=12 D=13 E=14 F=15
            i=0 C C*16^0
            i=1 8 8*16^1
            i=2 B B*16^2
            i=3 A A*16^3
            */
            if(isLetter(c)){
                num+=(c-'A'+10)*Math.pow(16,i);
            }else{
                num+=(c-'0')*Math.pow(16,i);
            }
        }
        return num;
    }
    public static boolean isLetter(char c){
        return c>='A'&&c<='F';
    }
}

第四章的题型