30秒快速编码

灵感来源: 30秒快速编码, 这是一组可重复使用的、经过测试的、可粘贴的Java17兼容代码片段，您可以在30秒内或更短的时间内理解这些代码片段。 如果您有兴趣对此库进行贡献，请参阅 贡献说明.

算法

快速排序

 public static void quickSort(int[] arr, int left, int right) {  var pivotIndex = left + (right - left) / 2;  var pivotValue = arr[pivotIndex];  var i = left;  var j = right;  while (i <= j) {  while (arr[i] < pivotValue) {  i++;  }  while (arr[j] > pivotValue) {  j--;  }  if (i <= j) {  var tmp = arr[i];  arr[i] = arr[j];  arr[j] = tmp;  i++;  j--;  }  if (left < i) {  quickSort(arr, left, j);  }  if (right > i) {  quickSort(arr, i, right);  }  }  }

冒泡排序

 public static void bubbleSort(int[] arr) {  var lastIndex = arr.length - 1;   for(var j = 0; j < lastIndex; j++) {  for(var i = 0; i < lastIndex - j; i++) {  if(arr[i] > arr[i + 1]) {  var tmp = arr[i];  arr[i] = arr[i + 1];  arr[i + 1] = tmp;  }  }  }  }

选择排序

 public static void selectionSort(int[] arr) {  var len = arr.length;    for (var i = 0; i < len - 1; i++) {  var minIndex = i;    for (var j = i + 1; j < len; j++) {  if(arr[j] < arr[minIndex])  minIndex = j;  }    var tmp = arr[minIndex];  arr[minIndex] = arr[i];  arr[i] = tmp;  }  }

插入排序

 public static void insertionSort(int[] arr) {  for (var i = 1; i < arr.length; i++) {  var tmp = arr[i];  var j = i - 1;   while (j >= 0 && arr[j] > tmp) {  arr[j + 1] = arr[j];  j--;  }  arr[j + 1] = tmp;  }  }

计数排序

 public static void countingSort(int[] arr) {  var max = Arrays.stream(arr).max().getAsInt();   var count = new int[max + 1];   for (var num : arr) {  count[num]++;  }   for (var i = 1; i <= max; i++) {  count[i] += count[i - 1];  }   var sorted = new int[arr.length];  for (var i = arr.length - 1; i >= 0; i--) {  var cur = arr[i];  sorted[count[cur] - 1] = cur;  count[cur]--;  }   var index = 0;  for (var num : sorted) {  arr[index++] = num;  }  }

数组

通用双数组串联

 public static <T> T[] arrayConcat(T[] first, T[] second) {  var result = Arrays.copyOf(first, first.length + second.length);  System.arraycopy(second, 0, result, first.length, second.length);  return result;  }

通用多数组串联

 public static <T> T[] nArrayConcat(T[] first, T[]... rest) {  var totalLength = first.length;  for (var array : rest) {  totalLength += array.length;  }  var result = Arrays.copyOf(first, totalLength);  var offset = first.length;  for (var array : rest) {  System.arraycopy(array, 0, result, offset, array.length);  offset += array.length;  }  return result;  }

计算数组的所有元素是否相等

 public static <T> boolean allEqual(T[] arr) {  return Arrays.stream(arr).distinct().count() == 1;  }

计算整数数组的平均值

 public static double arrayMean(int[] arr) {  return (double) Arrays.stream(arr).sum() / arr.length;  }

计算整数数组的中值

 public static double arrayMedian(int[] arr) {  Arrays.sort(arr);  var mid = arr.length / 2;  return arr.length % 2 != 0 ? (double) arr[mid] : (double) (arr[mid] + arr[mid - 1]) / 2;  }

Mode in Array

 public static int modeArray(int arr[])  {  int mode=0,maxcount=0;   for(int i=0;i<arr.length;i++)  {  int count=0;   for(int j=0;j<arr.length;j++)  {  if(arr[i]==arr[j])  count++;  }  if(count>maxcount)  {  maxcount=count;  mode=arr[i];  }  }  return mode;  }

计算整数数组的和

 public static int arraySum(int[] arr) {  return Arrays.stream(arr).sum();  }

计算整数数组的最大值

 public static int findMax(int[] arr) {  return Arrays.stream(arr).reduce(Integer.MIN_VALUE, Integer::max);  }

编码

Base64编码字符串

 public static String encodeBase64(String input) {  return Base64.getEncoder().encodeToString(input.getBytes());  }

Base64解码字符串

 public static String decodeBase64(String input) {  return new String(Base64.getDecoder().decode(input.getBytes()));  }

文件

列出目录

 public static File[] listDirectories(String path) {  return new File(path).listFiles(File::isDirectory);  }

列出目录中的文件

 public static File[] listFilesInDirectory(final File folder) {  return folder.listFiles(File::isFile);  }

递归列出目录中的文件

 public static List<File> listAllFiles(String path) {  var all = new ArrayList<File>();  var list = new File(path).listFiles();   if (list != null) { // 访问错误时, list为null  for (var f : list) {  if (f.isDirectory()) {  all.addAll(listAllFiles(f.getAbsolutePath()));  } else {  all.add(f.getAbsoluteFile());  }  }  }  return all;  }

将文件中的行读取到字符串列表

 public static List<String> readLines(String filename) throws IOException {  return Files.readAllLines(new File(filename).toPath());  }

压缩单个文件为Zip文件

 public static void zipFile(String srcFilename, String zipFilename) throws IOException {  var srcFile = new File(srcFilename);  try (  var fileOut = new FileOutputStream(zipFilename);  var zipOut = new ZipOutputStream(fileOut);  var fileIn = new FileInputStream(srcFile);  ) {  var zipEntry = new ZipEntry(srcFile.getName());  zipOut.putNextEntry(zipEntry);  final var bytes = new byte[1024];  int length;  while ((length = fileIn.read(bytes)) >= 0) {  zipOut.write(bytes, 0, length);  }  }  }

压缩多个文件为Zip文件

 public static void zipFiles(String[] srcFilenames, String zipFilename) throws IOException {  try (  var fileOut = new FileOutputStream(zipFilename);  var zipOut = new ZipOutputStream(fileOut);  ) {  for (var i=0; i<srcFilenames.length; i++) {  var srcFile = new File(srcFilenames[i]);  try (var fileIn = new FileInputStream(srcFile)) {  var zipEntry = new ZipEntry(srcFile.getName());  zipOut.putNextEntry(zipEntry);  final var bytes = new byte[1024];  int length;  while ((length = fileIn.read(bytes)) >= 0) {  zipOut.write(bytes, 0, length);  }  }  }  }  }

压缩文件夹为Zip文件

 public static void zipDirectory (String srcDirectoryName, String zipFileName) throws IOException {  var srcDirectory = new File(srcDirectoryName);  try (  var fileOut = new FileOutputStream(zipFileName);  var zipOut = new ZipOutputStream(fileOut)  ) {  zipFile(srcDirectory, srcDirectory.getName(), zipOut);  }  }  public static void zipFile(File fileToZip, String fileName, ZipOutputStream zipOut)   throws IOException {  if (fileToZip.isHidden()) { // 忽略隐藏的文件  return;  }  if (fileToZip.isDirectory()) {  if (fileName.endsWith("/")) {  zipOut.putNextEntry(new ZipEntry(fileName)); // 稍后压缩  zipOut.closeEntry();  } else {  // 在执行解压缩操作时，显式添加"/"标记以保留结构  zipOut.putNextEntry(new ZipEntry(fileName + "/"));  zipOut.closeEntry();  }  var children = fileToZip.listFiles();  for (var childFile : children) { // 递归地将函数应用于所有子级  zipFile(childFile, fileName + "/" + childFile.getName(), zipOut);  }  return;  }  try (  var fis = new FileInputStream(fileToZip) // 只能是一个文件，开始压缩  ) {  var zipEntry = new ZipEntry(fileName);  zipOut.putNextEntry(zipEntry);  var bytes = new byte[1024];  var length = 0;  while ((length = fis.read(bytes)) >= 0) {  zipOut.write(bytes, 0, length);  }  }  }

数学

Even or Odd

 public static String evenodd(int num)  {  if(num%2==0)  return "even";  else  return "odd";  }

斐波那契

 public static int fibonacci(int n) {  if (n <= 1) {  return n;  } else {  return fibonacci(n - 1) + fibonacci(n - 2);  }  }

迭代斐波那契

 public static int iterativeFibonacci(int number) {  List<Integer> list = new ArrayList<>();  list.add(0);  list.add(1);  for (int i = 2; i < number + 1; i++) {  list.add(list.get(i - 2) + list.get(i - 1));  }  return list.get(number);  }

阶乘

 public static int factorial(int number) {  var result = 1;  for (var factor = 2; factor <= number; factor++) {  result *= factor;  }  return result;  }

递归阶乘

 public static int recursiveFactorial(int number) {  var initial = 0;  if (number == initial) {  return initial + 1;  }  return number * recursiveFactorial(number - 1);  }

半正矢公式

 // 点所在的球体半径，在本例中为地球  private static final double SPHERE_RADIUS_IN_KM = 6372.8;   public static double findHaversineDistance(double latA, double longA, double latB, double longB) {  if (!isValidLatitude(latA)  || !isValidLatitude(latB)  || !isValidLongitude(longA)  || !isValidLongitude(longB)) {  throw new IllegalArgumentException();  }   // 计算纬度和经度差  var latitudeDiff = Math.toRadians(latB - latA);  var longitudeDiff = Math.toRadians(longB - longA);   var latitudeA = Math.toRadians(latA);  var latitudeB = Math.toRadians(latB);   // 根据哈弗辛公式(haversine)计算距离  var a = Math.pow(Math.sin(latitudeDiff / 2), 2)  + Math.pow(Math.sin(longitudeDiff / 2), 2) * Math.cos(latitudeA) * Math.cos(latitudeB);  var c = 2 * Math.asin(Math.sqrt(a));  return SPHERE_RADIUS_IN_KM * c;  }   // 检查有效纬度值  private static boolean isValidLatitude(double latitude) {  return latitude >= -90 && latitude <= 90;  }   // 检查有效的经度值  private static boolean isValidLongitude(double longitude) {  return longitude >= -180 && longitude <= 180;  }

抽奖

 public static Integer[] performLottery(int numNumbers, int numbersToPick) {  var numbers = new ArrayList<Integer>();  for(var i = 0; i < numNumbers; i++) {  numbers.add(i+1);  }   Collections.shuffle(numbers);  return numbers.subList(0, numbersToPick).toArray(new Integer[numbersToPick]);  }

Luhn(模10)算法

public static int calculateLuhnChecksum(long num) {  if (num < 0) {  throw new IllegalArgumentException("Non-negative numbers only.");  }  final var numStr = String.valueOf(num);   var sum = 0;  var isOddPosition = true;  // 我们从右到左循环numStr中的数字。  for (var i = numStr.length() - 1; i >= 0; i--) {  final var digit = Integer.parseInt(Character.toString(numStr.charAt(i)));  final var substituteDigit = (isOddPosition ? 2 : 1) * digit;   final var tensPlaceDigit = substituteDigit / 10;  final var onesPlaceDigit = substituteDigit % 10;  sum += tensPlaceDigit + onesPlaceDigit;   isOddPosition = !isOddPosition;  }  final var checksumDigit = (10 - (sum % 10)) % 10;  // Outermost modulus handles edge case `num = 0`.  return checksumDigit;  }

SquareRoot of a Number

static double sqrt(int num,int p) //p-precision(till how many decimal numbers we want)  {  int start=0,end=num;  double root=0.0;   while(start<=end)  {  int mid=start+(end-start)/2;   if((mid*mid)>num)  end=mid-1;  else if((mid*mid)<num)  start=mid+1;  else  return mid;  }  //root=end;  double incr=0.1;   for(int i=0;i<p;i++)  {  while(root*root < num)  root=root+incr;   root=root-incr;  incr=incr/10;  }   return root;  }

最大公约数

 public static int gcd(int a, int b) {   if (b == 0)   return a;   return gcd(b, a % b);   }

素数

 public static boolean isPrime(int number) {  if (number < 3) {  return true;  }   // 检查n是否为2的倍数  if (number % 2 == 0) {  return false;  }   // 如果没有，只看基数  for (var i = 3; i * i <= number; i += 2) {  if (number % i == 0) {  return false;  }  }  return true;  }

自然数二进制转换

 public static String toBinary(long naturalNumber) {  if (naturalNumber < 0) {  throw new NumberFormatException("Negative Integer, this snippet only accepts "  + "positive integers");  }  if (naturalNumber == 0) {  return "0";  }  final Stack<Long> binaryBits =  Stream.iterate(naturalNumber, n -> n > 0, n -> n / 2).map(n -> n % 2)  .collect(Stack::new, Stack::push, Stack::addAll);  return Stream.generate(binaryBits::pop)  .limit(binaryBits.size()).map(String::valueOf).collect(Collectors.joining());  }    public static Long fromBinary(String binary) {  binary.chars().filter(c -> c != '0' && c != '1').findFirst().ifPresent(in -> {  throw new NumberFormatException(  "Binary string contains values other than '0' and '1'");  });  return IntStream.range(0, binary.length())  .filter(in -> binary.charAt(binary.length() - 1 - in) == '1')  .mapToLong(in -> ((long) 0b1) << in).sum();  }

多媒体

截屏

 public static void captureScreen(String filename) throws AWTException, IOException {  var screenSize = Toolkit.getDefaultToolkit().getScreenSize();  var screenRectangle = new Rectangle(screenSize);  var robot = new Robot();  var image = robot.createScreenCapture(screenRectangle);  ImageIO.write(image, "png", new File(filename));  }

网络

HTTP GET

 public static HttpResponse<String> httpGet(String uri) throws Exception {  var client = HttpClient.newHttpClient();  var request = HttpRequest.newBuilder()  .uri(URI.create(uri))  .build();  return client.send(request, BodyHandlers.ofString());  }

HTTP POST

 public static HttpResponse<String> httpPost(String address, HashMap<String,String> arguments)   throws IOException, InterruptedException {  var sj = new StringJoiner("&");  for(var entry : arguments.entrySet()) {  sj.add(URLEncoder.encode(entry.getKey(), "UTF-8") + "="  + URLEncoder.encode(entry.getValue(), "UTF-8"));  }   var out = sj.toString().getBytes(StandardCharsets.UTF_8);  var request = HttpRequest.newBuilder()  .uri(URI.create(address))  .headers("Content-Type", "application/x-www-form-urlencoded; charset=UTF-8")  .POST(BodyPublishers.ofByteArray(out))  .build();   return HttpClient.newHttpClient().send(request, BodyHandlers.ofString());  }

字符串

回文检查

 public static boolean isPalindrome(String s) {  for (int i = 0, j = s.length() - 1; i < j; i++, j--) {  while (i < j && !Character.isLetter(s.charAt(i))) {  i++;  }  while (i < j && !Character.isLetter(s.charAt(j))) {  j--;  }   if (Character.toLowerCase(s.charAt(i)) != Character.toLowerCase(s.charAt(j))) {  return false;  }  }   return true;  }

反转字符串

 public static String reverseString(String s) {  return new StringBuilder(s).reverse().toString();  }

字符串转换到日期

 public static Date stringToDate(String date, String format) throws ParseException {  var simpleDateFormat = new SimpleDateFormat(format);  return simpleDateFormat.parse(date);  }

重组子串检查

 public boolean isAnagram(String s1, String s2) {   var l1 = s1.length();  var l2 = s2.length();  var arr1 = new int[256];  var arr2 = new int[256];  if (l1 != l2) {  return false;  }    for (var i = 0; i < l1; i++) {  arr1[s1.charAt(i)]++;  arr2[s2.charAt(i)]++;  }   return Arrays.equals(arr1, arr2);  }

计算Levenshtein距离

 public static int findLevenshteinDistance(String word1, String word2) {  // 如果word2为空，则删除  int[][] ans = new int[word1.length() + 1][word2.length() + 1];  for (int i = 0; i <= word1.length(); i++) {  ans[i][0] = i;  }   // 如果word1为空，则添加  for (int i = 0; i <= word2.length(); i++) {  ans[0][i] = i;  }   // 都不为空  for (int i = 1; i <= word1.length(); i++) {  for (int j = 1; j <= word2.length(); j++) {  int min = Math.min(Math.min(ans[i][j - 1], ans[i - 1][j]), ans[i - 1][j - 1]);  ans[i][j] = word1.charAt(i - 1) == word2.charAt(j - 1) ? ans[i - 1][j - 1] : min + 1;  }  }  return ans[word1.length()][word2.length()];  }

比较版本

 public static int compareVersion(String v1, String v2) {  Function<String, String[]> getVersionComponents = version -> version.replaceAll(".*?((?<!\\w)\\d+([.-]\\d+)*).*", "$1", "$1").split("\\.");   var components1 = getVersionComponents.apply(v1);  var components2 = getVersionComponents.apply(v2);  int length = Math.max(components1.length, components2.length);   for (int i = 0; i < length; i++) {  Integer c1 = i < components1.length ? Integer.parseInt(components1[i]) : 0;  Integer c2 = i < components2.length ? Integer.parseInt(components2[i]) : 0;  int result = c1.compareTo(c2);  if (result != 0) {  return result;  }  }  return 0;  }

获取相同字母

 public static String getCommonLetters(String firstStr, String secondStr) {  Set<String> commonLetters = new HashSet<>();  for (Character currentCharacter : firstStr.toCharArray()) {  if (isCommonLetter(secondStr, currentCharacter)) {  commonLetters.add(currentCharacter.toString());  }  }  return String.join(" ", commonLetters);  }   private static boolean isCommonLetter(String str, Character character) {  return str.contains(character.toString()) && Character.isLetter(character);  }

计算某个字符出现的最大次数

 public static int getMaxCharacterCount(String str, char character) {  int characterCount = 0;  int maxCharacterCount = 0;  for (int i = 0; i < str.length(); i++) {  if ((str.charAt(i)) == character) {  characterCount++;  maxCharacterCount = Math.max(maxCharacterCount, characterCount);  } else {  characterCount = 0;  }  }  return maxCharacterCount;  }

从字符串中删除重复字符

 public static String removeDuplicateCharacters(String str) {  char[] charsOfStr = str.toCharArray();  Set<String> uniqueCharacters = new HashSet<>();  for (char character : charsOfStr) {  uniqueCharacters.add(String.valueOf(character));  }  return String.join("", uniqueCharacters);  }

类

获取公开的方法名称列表

 public static List<String> getAllMethods(final Class<?> cls) {  return Arrays.stream(cls.getDeclaredMethods())  .map(Method::getName)  .collect(Collectors.toList());  }

获取公开的字段名称列表

 public static List<String> getAllFieldNames(final Class<?> cls) {  return Arrays.stream(cls.getFields())  .map(Field::getName)  .collect(Collectors.toList());  }

获取所有的字段名称列表

 public static List<String> getAllFieldNames(final Class<?> cls) {  var fields = new ArrayList<String>();  var currentCls = cls;  while (currentCls != null) {  fields.addAll(  Arrays.stream(currentCls.getDeclaredFields())  .filter(field -> !field.isSynthetic())  .map(Field::getName)  .collect(Collectors.toList()));  currentCls = currentCls.getSuperclass();  }  return fields;  }

无参构造实例化

 public static Object createObject(String cls)  throws NoSuchMethodException,  IllegalAccessException,  InvocationTargetException,  InstantiationException,  ClassNotFoundException {  var objectClass = Class.forName(cls);  var objectConstructor = objectClass.getConstructor();  return objectConstructor.newInstance();  }

I/O(输入/输出)

按流读取文件

 public static List<String> readFile(String fileName) throws FileNotFoundException {  try (Stream<String> stream = new BufferedReader(new FileReader(fileName)).lines()) {  return stream.collect(Collectors.toList());  }  }

输入流到字符串

 public static String inputStreamToString(InputStream inputStream) throws IOException {  try (var reader = new BufferedReader(new InputStreamReader(inputStream))) {  var stringBuilder = new StringBuilder();  var data = reader.read();    while (data != -1) {  stringBuilder.append((char) data);  data = reader.read();  }  return stringBuilder.toString();  }  }

线程

创建线程数固定的线程池

 public static ExecutorService createFixedThreadPool() {  return Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());  }

日期

计算no天后的日期

 public static Date addDaysToDate(Date date, int noOfDays){  if(date!=null){  Calendar cal = Calendar.getInstance();  cal.setTime(date);  cal.add(Calendar.DAY_OF_MONTH, noOfDays);  return cal.getTime();  }  return null;  }

计算no天后的本地日期

 public static LocalDate addDaysToLocalDate(LocalDate date, long noOfDays){  return date!=null ? date.plusDays(noOfDays) : null;  }