diff --git a/src/main/java/com/example/demo/arraySeries/MaxLengthStr.java b/src/main/java/com/example/demo/arraySeries/MaxLengthStr.java
new file mode 100644
index 0000000..01a37cd
--- /dev/null
+++ b/src/main/java/com/example/demo/arraySeries/MaxLengthStr.java
@@ -0,0 +1,62 @@
+package com.example.demo.arraySeries;
+
+/**
+ * 最长公共前缀
+ * 说明：
+ *  1. 所有输入只包含小写字母 a-z
+ *  2. 如果不存在公共前缀，则返回""
+ */
+public class MaxLengthStr {
+
+    public static String longestCommonPrefix(String[] strs) {
+        if (strs == null || strs.length == 0) {
+            return "";
+        }
+        String prefix = strs[0];
+        int count = strs.length;
+        for (int i = 1; i < count; i++) {
+            prefix = longestCommonPrefix(prefix, strs[i]);
+            if (prefix.length() == 0) {
+                break;
+            }
+        }
+        return prefix;
+    }
+
+    public static String longestCommonPrefix(String str1, String str2) {
+        int length = Math.min(str1.length(), str2.length());
+        int index = 0;
+        while (index < length && str1.charAt(index) == str2.charAt(index)) {
+            index++;
+        }
+        return str1.substring(0, index);
+    }
+
+    public static String demo(String[] strs){
+
+        if(strs == null || strs.length == 0){
+            return "";
+        }
+        String prefix = strs[0];
+        String outStr = "";
+        for (int i =0; i<strs.length; i++){
+            String str = strs[i];
+            int lengt = Math.min(prefix.length(),strs[i].length());
+            int index = lengt-1;
+            while (index < lengt && prefix.charAt(index) ==  str.charAt(index)){
+                index++;
+            }
+            prefix = prefix.substring(0,index);
+        }
+        return prefix;
+    }
+    public static void main(String[] args) {
+
+        String [] str = {"ddog","dracecar","dcar"};
+        String outStr = demo(str);
+//        String outStr = "ddog";
+        System.out.println("commonPrefix = [" + outStr + "]");
+
+    }
+
+}
diff --git a/src/main/java/com/example/demo/arraySeries/TheIntersectionOfTwoNumbers.java b/src/main/java/com/example/demo/arraySeries/TheIntersectionOfTwoNumbers.java
index 10650d1..9ad7ea1 100644
--- a/src/main/java/com/example/demo/arraySeries/TheIntersectionOfTwoNumbers.java
+++ b/src/main/java/com/example/demo/arraySeries/TheIntersectionOfTwoNumbers.java
@@ -5,6 +5,12 @@
 
 import java.util.*;
 
+/**
+ * 两个数组的交集
+ * 说明：
+ *  1. 输出结果中每个元素出现的次数，应与元素在两个数组中出现的次数一致。
+ *  2. 我们可以不考虑输出结果的顺序。
+ */
 public class TheIntersectionOfTwoNumbers {
 
 
diff --git a/src/main/java/com/example/demo/arraySeries/explain.md b/src/main/java/com/example/demo/arraySeries/explain.md
index 6a5a5a4..60d430a 100644
--- a/src/main/java/com/example/demo/arraySeries/explain.md
+++ b/src/main/java/com/example/demo/arraySeries/explain.md
@@ -1,2 +1,3 @@
 # 说明 - 数组系列
 1. TheIntersectionOfTwoNumbers - 两个数的交集  
+2. MaxLengthStr - 最长公共前缀
\ No newline at end of file