diff --git a/L2023111055_2_Test.java b/L2023111055_2_Test.java
new file mode 100644
index 00000000..5ffc1869
--- /dev/null
+++ b/L2023111055_2_Test.java
@@ -0,0 +1,39 @@
+package com.ai;
+
+import org.junit.Test;
+
+
+import static org.junit.Assert.assertEquals;
+
+public class L2023111055_2_Test{
+
+    @Test
+    public void testSolution2()
+    {
+        Solution2 solution = new Solution2();
+
+        // 测试目的：验证方法能否正确处理无重复字母的字符串
+        // 测试用例：输入 "abc"，期望输出 "abc"
+        assertEquals("abc", solution.removeDuplicateLetters("abc"));
+
+        // 测试目的：验证方法能否正确处理有重复字母的字符串
+        // 测试用例：输入 "bcabc"，期望输出 "abc"
+        assertEquals("abc", solution.removeDuplicateLetters("bcabc"));
+
+        // 测试目的：验证方法能否正确处理包含多个重复字母的字符串
+        // 测试用例：输入 "cbacdcbc"，期望输出 "acdb"
+        assertEquals("acdb", solution.removeDuplicateLetters("cbacdcbc"));
+
+        // 测试目的：验证方法能否正确处理空字符串
+        // 测试用例：输入 ""，期望输出 ""
+        assertEquals("", solution.removeDuplicateLetters(""));
+
+        // 测试目的：验证方法能否正确处理单个字符的字符串
+        // 测试用例：输入 "a"，期望输出 "a"
+        assertEquals("a", solution.removeDuplicateLetters("a"));
+
+        // 测试目的：验证方法能否正确处理所有字符相同的字符串
+        // 测试用例：输入 "aaa"，期望输出 "a"
+        assertEquals("a", solution.removeDuplicateLetters("aaa"));
+    }
+}
\ No newline at end of file
diff --git a/OSSDP-Lab2.iml b/OSSDP-Lab2.iml
new file mode 100644
index 00000000..b107a2dd
--- /dev/null
+++ b/OSSDP-Lab2.iml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<module type="JAVA_MODULE" version="4">
+  <component name="NewModuleRootManager" inherit-compiler-output="true">
+    <exclude-output />
+    <content url="file://$MODULE_DIR$">
+      <sourceFolder url="file://$MODULE_DIR$" isTestSource="false" />
+    </content>
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>
\ No newline at end of file
diff --git a/Solution2.java b/Solution2.java
index 3218bd12..623c4c71 100644
--- a/Solution2.java
+++ b/Solution2.java
@@ -1,5 +1,7 @@
-/**
- * @description:
+package com.ai;
+
+/*
+ * /description:
  *
  * 给你一个字符串 s ，请你去除字符串中重复的字母，使得每个字母只出现一次。需保证 返回结果的字典序最小（要求不能打乱其他字符的相对位置）。
  *
@@ -16,18 +18,18 @@
  * 1 <= s.length <= 104
  * s 由小写英文字母组成
  */
-class Solution2 {
+public class Solution2 {
     public String removeDuplicateLetters(String s) {
         boolean[] vis = new boolean[25];
         int[] num = new int[25];
         for (int i = 0; i < s.length(); i++) {
-            num[s.charAt(i) - ' ']++;
+            num[s.charAt(i) - 'a']++;
         }
 
         StringBuffer sb = new StringBuffer();
-        for (int i = 0; i < s.length()+1; i++) {
+        for (int i = 0; i < s.length(); i++) {
             char ch = s.charAt(i);
-            if (!vis[ch - ' ']) {
+            if (!vis[ch - 'a']) {
                 while (sb.length() > 0 && sb.charAt(sb.length() - 1) > ch) {
                     if (num[sb.charAt(sb.length() - 1) - 'a'] > 0) {
                         vis[sb.charAt(sb.length() - 1) - 'a'] = false;
@@ -39,7 +41,7 @@ public String removeDuplicateLetters(String s) {
                 vis[ch - 'a'] = true;
                 sb.append(ch);
             }
-            num[ch - 'a'] += 1;
+            num[ch - 'a'] -= 1;
         }
         return sb.toString();
     }