diff --git a/src/main/java/com/cool/hot100/stack/Num20.java b/src/main/java/com/cool/hot100/stack/Num20.java
new file mode 100644
index 0000000..88c535b
--- /dev/null
+++ b/src/main/java/com/cool/hot100/stack/Num20.java
@@ -0,0 +1,41 @@
+package com.cool.hot100.stack;
+
+import org.junit.Test;
+
+import java.util.*;
+
+/**
+ * Created with IntelliJ IDEA.
+ *
+ * @Author: Cool
+ * @Date: 2024/09/16/2:57
+ * DayNumber 3
+ * Hard 1
+ * Level 3
+ */
+public class Num20 {
+
+
+    public boolean isValid(String s) {
+        Stack<Character> stack = new Stack<>();
+        char[] chars = s.toCharArray();
+        for (char aChar : chars) {
+            if(aChar=='('){
+                stack.push(')');
+            }else if(aChar=='{'){
+                stack.push('}');
+            }else if(aChar=='['){
+                stack.push(']');
+            }else if(stack.isEmpty()||stack.pop()!=aChar){
+                return false;
+            }
+        }
+        return stack.isEmpty();
+    }
+
+    @Test
+    public void test() {
+        isValid("()");
+    }
+
+}