diff --git a/src/main/java/array/RemoveDuplicates.java b/src/main/java/array/RemoveDuplicates.java
index 9995df2..43d9be5 100644
--- a/src/main/java/array/RemoveDuplicates.java
+++ b/src/main/java/array/RemoveDuplicates.java
@@ -13,8 +13,25 @@ package array;
 
  * 链接：https://leetcode.cn/problems/remove-duplicates-from-sorted-array/
  */
+//二刷会做
 public class RemoveDuplicates {
     //很啰嗦
+
+    /**
+     * 第一轮遍历（标记重复元素）​​
+     * pre 指针记录上一个有效元素位置
+     * 遇到重复值时：
+     * 将当前元素标记为 invalid（Integer.MIN_VALUE）
+     * deleted 计数器记录删除数量
+     * 非重复时：移动 pre 指针
+     * ​第二轮遍历（填充有效元素）​​
+     * 找到被标记为 invalid 的位置
+     * 从 start 或当前位置向后搜索第一个有效元素
+     * 交换/填充有效值到前面
+     * ​返回结果​
+     * 最终有效长度 = 原长度 - 删除数量
+
+     */
     public int removeDuplicates2(int[] nums) {
         int pre=0,deleted=0,start=0,invalid=Integer.MIN_VALUE;
         for (int i = 1; i < nums.length; i++) {
diff --git a/src/main/java/array/RemoveDuplicates2.java b/src/main/java/array/RemoveDuplicates2.java
index 23e020e..ba91e6f 100644
--- a/src/main/java/array/RemoveDuplicates2.java
+++ b/src/main/java/array/RemoveDuplicates2.java
@@ -11,6 +11,7 @@ package array;
 
  * 链接：https://leetcode.cn/problems/remove-duplicates-from-sorted-array-ii/
  */
+//二刷会做
 public class RemoveDuplicates2 {
     //自己写的
     public int removeDuplicates(int[] nums) {
diff --git a/src/main/java/dynamic_programming/LongestCommonSubsequence.java b/src/main/java/dynamic_programming/LongestCommonSubsequence.java
index 901b5e5..dd67c7d 100644
--- a/src/main/java/dynamic_programming/LongestCommonSubsequence.java
+++ b/src/main/java/dynamic_programming/LongestCommonSubsequence.java
@@ -15,6 +15,31 @@ package dynamic_programming;
  */
 //二刷会做
 public class LongestCommonSubsequence {
+    public int longestCommonSubsequence2(String text1, String text2) {
+        int len1=text1.length(),len2=text2.length();
+        int[][]dp=new int[len1+1][len2+1];
+        for (int i = 1; i <= len1; i++) {
+            for (int j = 1; j <= len2; j++) {
+                if(text1.charAt(i-1)==text2.charAt(j-1))
+                    dp[i][j]=dp[i-1][j-1]+1;
+                else
+                    dp[i][j]=Math.max(dp[i-1][j],dp[i][j-1]);
+            }
+        }
+        return dp[len1][len2];
+    }
+
+
+
+
+
+
+
+
+
+
+
+
     public int longestCommonSubsequence(String text1, String text2) {
         int n=text1.length(),m=text2.length();
         int[][]dp=new int[n+1][m+1];
diff --git a/src/main/java/dynamic_programming/LongestPalindrome.java b/src/main/java/dynamic_programming/LongestPalindrome.java
index 3a05a77..352cbda 100644
--- a/src/main/java/dynamic_programming/LongestPalindrome.java
+++ b/src/main/java/dynamic_programming/LongestPalindrome.java
@@ -1,4 +1,7 @@
 package dynamic_programming;
+
+import java.util.Arrays;
+
 /**
  * 题目： 5. 最长回文子串 (longestPalindrome)
  * 描述：给你一个字符串 s，找到 s 中最长的 回文 子串。
@@ -11,7 +14,9 @@ package dynamic_programming;
 
  * 链接：https://leetcode.cn/problems/longest-palindromic-substring/
  */
+//二刷不会
 public class LongestPalindrome {
+
     public String longestPalindrome(String s) {
         int n = s.length();
         if (n < 2) return s;
@@ -35,4 +40,51 @@ public class LongestPalindrome {
         }
         return s.substring(start, start + maxLen);
     }
+    public String longestPalindrome2(String s) {
+        int len = s.length();
+        if (len < 2) {
+            return s;
+        }
+
+        int maxLen = 1;
+        int begin = 0;
+        // dp[i][j] 表示 s[i..j] 是否是回文串
+        boolean[][] dp = new boolean[len][len];
+        // 初始化：所有长度为 1 的子串都是回文串
+        for (int i = 0; i < len; i++) {
+            dp[i][i] = true;
+        }
+
+        char[] charArray = s.toCharArray();
+        // 递推开始
+        // 先枚举子串长度
+        for (int L = 2; L <= len; L++) {
+            // 枚举左边界，左边界的上限设置可以宽松一些
+            for (int i = 0; i < len; i++) {
+                // 由 L 和 i 可以确定右边界，即 j - i + 1 = L 得
+                int j = L + i - 1;
+                // 如果右边界越界，就可以退出当前循环
+                if (j >= len) {
+                    break;
+                }
+
+                if (charArray[i] != charArray[j]) {
+                    dp[i][j] = false;
+                } else {
+                    if (j - i < 3) {
+                        dp[i][j] = true;
+                    } else {
+                        dp[i][j] = dp[i + 1][j - 1];
+                    }
+                }
+
+                // 只要 dp[i][L] == true 成立，就表示子串 s[i..L] 是回文，此时记录回文长度和起始位置
+                if (dp[i][j] && j - i + 1 > maxLen) {
+                    maxLen = j - i + 1;
+                    begin = i;
+                }
+            }
+        }
+        return s.substring(begin, begin + maxLen);
+    }
 }
diff --git a/src/main/java/dynamic_programming/MaxUncrossedLines.java b/src/main/java/dynamic_programming/MaxUncrossedLines.java
index 497f0cf..5cff361 100644
--- a/src/main/java/dynamic_programming/MaxUncrossedLines.java
+++ b/src/main/java/dynamic_programming/MaxUncrossedLines.java
@@ -19,7 +19,9 @@ package dynamic_programming;
  * 链接：https://leetcode.cn/problems/uncrossed-lines/
  */
 //转为求最长子序列
+//二刷会做
 public class MaxUncrossedLines {
+
     public int maxUncrossedLines(int[] nums1, int[] nums2) {
         int len1 = nums1.length;
         int len2 = nums2.length;