13 递归练习

递归练习：

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Scanner;

public class Teat1 {

    public static void main(String[] args) throws IOException {
        // 从键盘接收一个文件夹路径,统计该文件夹大小
        // 文件夹内容删除
//        File dir = getFir();
//        System.out.println(getFileLength(dir));
        
        File src = getFir();
//        File dest = getFir();
//        if (src.equals(dest)) {
//            System.out.println("目标文件夹是源文件夹得子文件夹");
//        }else {            
//            copy(src,dest);
//        }
        printLev(src, 0);
    }
    public static void printLev(File dir,int lev) {
        File[] subFiles = dir.listFiles();
        for (File subFile : subFiles) {
            for (int i = 0; i <= lev; i++) {
                System.out.print("	");
            }
            System.out.println(subFile);
            if (subFile.isDirectory()) {
                printLev(subFile, lev+1); // 不能为++lev或lev++，会改变lev

值
            }
        }
    }
    
    public static void copy(File src, File dest) throws IOException {
        // 一个文件夹中(包含内容)拷贝到另一个文件夹中
        File newDir = new File(dest,src.getName());
        newDir.mkdir();
        File[] subFiles = src.listFiles();
        for (File subFile : subFiles) {
            if (subFile.isFile()) {
                BufferedInputStream bis = new BufferedInputStream(new

FileInputStream(subFile));
                BufferedOutputStream bos = new BufferedOutputStream(new

FileOutputStream(new File(newDir,subFile.getName())));
                int b;
                while((b=bis.read())!=-1) {
                    bos.write(b);
                }
                bis.close();
                bos.close();
            }else { // 文件夹就递归调用
                copy(subFile, newDir);
            }
        }
        
    }

    public static File getFir() {
        while(true) {        
            Scanner scanner = new Scanner(System.in);
            System.out.println("请输入文件夹路径:");
            String line = scanner.nextLine();
            File file = new File(line);
            if (!file.exists()) {
                System.out.println("文件夹路径不存在，请重新输入");
            }else if (file.isFile()) {
                System.out.println("输入的是文件路径，请重新输入");
            }else {
                return file;
            }
        }
    }
    
    public static long getFileLength(File dir) {
        long len = 0;
        File[] subFiles = dir.listFiles();
        for (File subFile : subFiles) {
            if (subFile.isFile()) {
                len = len + subFile.length();
            }else {
                len = len + getFileLength(subFile);
            }
        }
        return len;
    }
    public static void delFile(File dir) {
        // 遍历删除文件，最后删除空的文件夹
        File[] subFiles = dir.listFiles();
        for (File subFile : subFiles) {
            if (subFile.isFile()) {
                subFile.delete();
            }else {
                delFile(subFile);
            }
        }
        dir.delete();  // 删除空文件夹
    }

}

public class Test2 {

    public static void main(String[] args) {
        // 斐波那契
        // 1 1 2 3 5 8
        int[] arr = new int[8];
        arr[0] = 1;
        arr[1] = 1;
        for (int i = 2; i < arr.length; i++) {
            arr[i] = arr[i-2] + arr[i-1];
        }
        System.out.println(arr[arr.length-1]);
        
        System.out.println(fun(8));
    }
    public static int fun(int num) {
        if (num==1 || num==2) {
            return 1;
        }else {
            return fun(num-2) + fun(num-1);
        }
    }
}

import java.math.BigInteger;

public class Test3 {

    public static void main(String[] args) {
        // 1000的阶乘所有零和尾部零的个数
        BigInteger bi1 = new BigInteger("1");
        for (int i = 1; i <= 1000; i++) {
            BigInteger bi2 = new BigInteger(i+"");
            bi1 = bi1.multiply(bi2); //相乘
        }
        String string = bi1.toString();
        int count = 0;
        for (int i = 0; i < string.length(); i++) {
            if ('0'==string.charAt(i)) {  // 索引
                count++;
            }
        }
        System.out.println(count); //472
        
        //尾部零的个数
        //通过反转
        StringBuffer stringBuffer = new StringBuffer(string);
        String string2 = stringBuffer.reverse().toString();  
        int count1 = 0;
        for (int i = 0; i < string2.length(); i++) {
            if ('0'!=string2.charAt(i)) {
                break;
            }else {
                count1++;
            }
        }
        System.out.println(count1); //249
        
        System.out.println(fun(20));
    }
    //尾部零的个数
    // 2*5*10  *12*15*20 *22*25*30
    // 1   2       3   4      5+1 6+1
    public static int fun(int num) {
        if(num > 0 && num < 5) {
            return 0;
        }else {
            return num / 5 + fun(num / 5);
        }
    }

}

import java.util.ArrayList;

public class Test4 {

    public static void main(String[] args) {
        // 约瑟夫环
        System.out.println(getLucklyNum(8));
    }
    public static int getLucklyNum(int num) {
        ArrayList<Integer> list = new ArrayList<>();
        for (int i = 1; i <= num; i++) {
            list.add(i);
        }
        int count = 1;
        for (int i = 0; list.size()!=1; i++) { //只要集合只留一个
            if (i==list.size()) { //i增长到集合最大的索引+1时
                i = 0;
            }
            if (count%3==0) {
                list.remove(i--); // 删除要更改i
            }
            count++;
        }
        return list.get(0);
    }
}