diff --git a/data/progress.md b/data/progress.md
index fab245b9..1c83970c 100644
--- a/data/progress.md
+++ b/data/progress.md
@@ -1,5 +1,8 @@
 # Progress
 
+# 2024-09-17
+- https://github.com/yennanliu/CS_basics/blob/master/doc/Leetcode_company_frequency-master/Google%206months-%20LeetCode.pdf
+
 # 2024-09-10
 - https://github.com/yennanliu/CS_basics/blob/master/doc/Leetcode_company_frequency-master/Google%206months-%20LeetCode.pdf
 
diff --git a/data/progress.txt b/data/progress.txt
index 3b5615fe..6732c399 100644
--- a/data/progress.txt
+++ b/data/progress.txt
@@ -1,3 +1,4 @@
+20240917: 
 20240910: 659
 20240909: 801,552
 20240908: 1057,1066,1110
diff --git a/leetcode_java/src/main/java/LeetCodeJava/String/EncodeAndDecodeStrings.java b/leetcode_java/src/main/java/LeetCodeJava/String/EncodeAndDecodeStrings.java
index c5c29ba4..2373bbac 100644
--- a/leetcode_java/src/main/java/LeetCodeJava/String/EncodeAndDecodeStrings.java
+++ b/leetcode_java/src/main/java/LeetCodeJava/String/EncodeAndDecodeStrings.java
@@ -1,6 +1,48 @@
 package LeetCodeJava.String;
 
 // https://leetcode.com/problems/encode-and-decode-strings/
+// https://leetcode.ca/all/271.html
+
+/**
+ * 271. Encode and Decode Strings
+ * Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and is decoded back to the original list of strings.
+ *
+ * Machine 1 (sender) has the function:
+ *
+ * string encode(vector<string> strs) {
+ *   // ... your code
+ *   return encoded_string;
+ * }
+ * Machine 2 (receiver) has the function:
+ * vector<string> decode(string s) {
+ *   //... your code
+ *   return strs;
+ * }
+ * So Machine 1 does:
+ *
+ * string encoded_string = encode(strs);
+ * and Machine 2 does:
+ *
+ * vector<string> strs2 = decode(encoded_string);
+ * strs2 in Machine 2 should be the same as strs in Machine 1.
+ *
+ * Implement the encode and decode methods.
+ *
+ *
+ *
+ * Note:
+ *
+ * The string may contain any possible characters out of 256 valid ascii characters. Your algorithm should be generalized enough to work on any possible characters.
+ * Do not use class member/global/static variables to store states. Your encode and decode algorithms should be stateless.
+ * Do not rely on any library method such as eval or serialize methods. You should implement your own encode/decode algorithm.
+ * Difficulty:
+ * Medium
+ * Lock:
+ * Prime
+ * Company:
+ * Bloomberg Google Microsoft Square Twitter
+ *
+ */
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -211,4 +253,30 @@ public List<String> decode_4(String s) {
         return decodedStrings;
     }
 
+    // V4
+    // https://leetcode.ca/2016-08-27-271-Encode-and-Decode-Strings/
+    public class Codec {
+
+        // Encodes a list of strings to a single string.
+        public String encode(List<String> strs) {
+            StringBuilder ans = new StringBuilder();
+            for (String s : strs) {
+                ans.append((char) s.length()).append(s);
+            }
+            return ans.toString();
+        }
+
+        // Decodes a single string to a list of strings.
+        public List<String> decode(String s) {
+            List<String> ans = new ArrayList<>();
+            int i = 0, n = s.length();
+            while (i < n) {
+                int size = s.charAt(i++);
+                ans.add(s.substring(i, i + size));
+                i += size;
+            }
+            return ans;
+        }
+    }
+
 }
diff --git a/leetcode_java/src/main/java/dev/workspace3.java b/leetcode_java/src/main/java/dev/workspace3.java
index 1d594520..93e97f25 100644
--- a/leetcode_java/src/main/java/dev/workspace3.java
+++ b/leetcode_java/src/main/java/dev/workspace3.java
@@ -7704,5 +7704,59 @@ public int compare(int[] o1, int[] o2) {
 //        return false;
 //    }
 
+    // LC 271
+    /**
+     *  exp 1:
+     *   input : ["", "helo"]
+     *   output : ["", "helo"]
+     *
+     *   encode : "?,helo"
+     *
+     *   exp 2:
+     *
+     *   input : ["helo", "world"]
+     *   output :  ["helo", "world"]
+     *
+     *   encode : "helo,world"
+     *
+     *
+     */
+    public class Codec {
+
+        // Encodes a list of strings to a single string.
+        public String encode(List<String> strs) {
+            //String res = null;
+            StringBuilder sb = new StringBuilder();
+            for (String x : strs){
+                if (x == null){
+                    sb.append("?");
+                    sb.append(",");
+                }else{
+                    sb.append(x);
+                    sb.append(",");
+                }
+            }
+            // remove last ","
+            return sb.deleteCharAt(sb.length()-1).toString();
+        }
+
+        // Decodes a single string to a list of strings.
+        public List<String> decode(String s) {
+            List<String> res = new ArrayList<>();
+            if (s == null){
+                return res;
+            }
+            for (String x : s.split(",")){
+                if (x.equals("?")){
+                    res.add("");
+                }else{
+                    res.add(x);
+                }
+            }
+            return res;
+        }
+    }
+
+
 
 }