Java中檢查字符串是否包含所有唯一字符

1. 概述

在本教程中，我們將學習各種技術來檢查字符串中存在的所有字符（包括非 ASCII 字符）是否唯一。此外，這裡討論的所有方法都不區分大小寫。

2. 暴力破解

這是最明顯的技術之一，但它有點粗糙，而且可能不是最有效的。我們將字符串中的字符相互比較：

public class UniqueCharChecker {
 public static boolean bruteForceCheck(String str) {
 char[] chars = str.toUpperCase().toCharArray();
 for (int i = 0; i < chars.length; i++) {
 for (int j = i + 1; j < chars.length; j++) {
 if(chars[i] == chars[j]) {
 return false;
 }
 }
 }
 return true;
 }
 }

讓我們為上面的方法編寫一些測試用例：

public class UniqueCharCheckerUnitTest {
 @Test
 public void givenUnique_whenBruteForceCheck_thenReturnTrue() {
 String[] sampleStrings = new String[]{"Justfewdi123", "$%&Hibusc", "Hibusc%$#", "მშვნიერ"};
 final String MSG = "Duplicate found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertTrue(MSG + " in " + sampleStr, UniqueCharChecker.checkV1(sampleStr)));
 }

 @Test
 public void givenNotUnique_whenBruteForceCheck_thenReturnFalse() {
 String[] sampleStrings = new String[]{"Justfewdif123", "$%&Hibushc", "Hibusuc%$#", "Hi%busc%$#", "მშვენიერი"};
 final String MSG = "Duplicate not found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertFalse(MSG + " in " + sampleStr, UniqueCharChecker.checkV1(sampleStr)));
 }
 }

2. 排序

所以這類似於暴力破解技術，但是這裡我們首先對tring中的字符進行排序，然後將它們與它們的鄰居進行比較，而不是與每個字符進行比較。我們來看看實現：

public static boolean sortAndThenCheck(String str) {
 char[] chars = str.toUpperCase().toCharArray();
 Arrays.sort(chars);
 for (int i = 0; i < chars.length - 1; i++) {
 if(chars[i] == chars[i+1]) {
 return false;
 }
 }
 return true;
 }

我們來測試一下：

@Test
 public void givenUnique_whenSortAndThenCheck_thenReturnTrue() {
 String[] sampleStrings = new String[]{"Justfewdi123", "$%&Hibusc", "Hibusc%$#", "მშვნიერ"};
 final String MSG = "Duplicate found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertTrue(MSG + " in " + sampleStr, UniqueCharChecker.checkV2(sampleStr)));
 }
 @Test
 public void givenNotUnique_whenSortAndThenCheck_thenReturnFalse() {
 String[] sampleStrings = new String[]{"Justfewdif123", "$%&Hibushc", "Hibusuc%$#", "Hi%busc%$#", "მშვენიერი"};
 final String MSG = "Duplicate not found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertFalse(MSG + " in " + sampleStr, UniqueCharChecker.checkV2(sampleStr)));
 }

3. HashSet

在這裡，我們利用java.util.Set to刪除重複字符：

public static boolean useSetCheck(String str) {
 char[] chars = str.toUpperCase().toCharArray();
 Set <Character> set = new HashSet <>();
 for (char c : chars) {
 set.add(c);
 }
 return set.size() == str.length();
 }

現在，讓我們看一下測試用例：

@Test
 public void givenUnique_whenUseSetCheck_thenReturnTrue() {
 String[] sampleStrings = new String[]{"Justfewdi123", "$%&Hibusc", "Hibusc%$#", "მშვნიერ" };
 final String MSG = "Duplicate found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertTrue(MSG + " in " + sampleStr, UniqueCharChecker.checkV3(sampleStr)));
 }
 @Test
 public void givenNotUnique_whenUseSetCheck_thenReturnFalse() {
 String[] sampleStrings = new String[]{"Justfewdif123", "$%&Hibushc", "Hibusuc%$#", "Hi%busc%$#", "მშვენიერი"};
 final String MSG = "Duplicate not found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertFalse(MSG + " in " + sampleStr, UniqueCharChecker.checkV3(sampleStr)));
 }

4.Java 流

此技術與上一節中使用的方法類似。但是，我們使用 Streams API 來創建Set.我們看一下實現：

public static boolean useStreamCheck(String str) {
 boolean isUnique = str.toUpperCase().chars()
 .mapToObj(c -> (char) c)
 .collect(Collectors.toSet())
 .size() == str.length();
 return isUnique;
 }

讓我們檢查一下單元測試：

@Test
 public void givenUnique_whenUseStreamCheck_thenReturnTrue() {
 String[] sampleStrings = new String[]{"Justfewdi123", "$%&Hibusc", "Hibusc%$#", "მშვნიერ" };
 final String MSG = "Duplicate found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertTrue(MSG + " in " + sampleStr, UniqueCharChecker.checkV1(sampleStr)));
 }
 @Test
 public void givenNotUnique_whenUseStreamCheck_thenReturnFalse() {
 String[] sampleStrings = new String[]{"Justfewdif123", "$%&Hibushc", "Hibusuc%$#", "Hi%busc%$#", "მშვენიერი"};
 final String MSG = "Duplicate not found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertFalse(MSG + " in " + sampleStr, UniqueCharChecker.checkV4(sampleStr)));
 }

5. StringUtils

基本上，在這裡，我們將使用 commons-lang StringUtils類中的containsIgnoreCase()方法：

public static boolean useStringUtilscheck(String str) {
 for (int i = 0; i < str.length(); i++) {
 String curChar = String.valueOf(str.charAt(i));
 String remainingStr = str.substring(i+1);
 if(StringUtils.containsIgnoreCase(remainingStr, curChar)) {
 return false;
 }
 }
 return true;
 }

我們來測試一下這個方法：

@Test
 public void givenUnique_whenUseStringUtilscheck_thenReturnTrue() {
 String[] sampleStrings = new String[]{"Justfewdi123", "$%&Hibusc", "Hibusc%$#", "მშვნიერ"};
 final String MSG = "Duplicate found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertTrue(MSG + " in " + sampleStr, UniqueCharChecker.checkV5(sampleStr)));
 }
 @Test
 public void givenNotUnique_whenUseStringUtilscheck_thenReturnFalse() {
 String[] sampleStrings = new String[]{"Justfewdif123", "$%&Hibushc", "Hibusuc%$#", "Hi%busc%$#", "მშვენიერი"};
 final String MSG = "Duplicate not found";
 Arrays.stream(sampleStrings)
 .forEach(sampleStr -> assertFalse(MSG + " in " + sampleStr, UniqueCharChecker.checkV5(sampleStr)));
 }

六，結論

在本教程中，我們看到了五種不同的方法來檢查字符串是否具有唯一字符。我們還得出結論，沒有現成的庫可用於解決此問題。

此處使用的代碼片段以及相關的 JUnit 測試用例可在 GitHub 上獲取。