Update README.md

Author: qanhnn12

README.md

@@ -23,7 +23,7 @@ Solutions for all free SQL challenges on Leetcode executed on MySQL and MS SQL S
 | 15 | [586. Customer Placing the Largest Number of Orders](https://leetcode.com/problems/customer-placing-the-largest-number-of-orders/) | [Link](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Easy/586.Customer-Placing-the-Largest-Number-of-Orders.sql) | 
 | 16 | [595. Big Countries](https://leetcode.com/problems/big-countries/) | [Link](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Easy/595.Big-Countries.sql) | 
 | 17 | [596. Classes More Than 5 Students](https://leetcode.com/problems/classes-more-than-5-students/) | [Link](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Easy/596.Classes-More-Than-5-Students.sql) | 
-| 18 | [601. Human Traffic of Stadium](https://leetcode.com/problems/human-traffic-of-stadium/) | [Link]([https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Human-Traffic-of-Stadium.sql](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Hard/601.Human-Traffic-of-Stadium.sql) | 
+| 18 | [601. Human Traffic of Stadium](https://leetcode.com/problems/human-traffic-of-stadium/) | [Link](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Human-Traffic-of-Stadium.sql](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Hard/601.Human-Traffic-of-Stadium.sql) | 
 | 19 | [607. Sales Person](https://leetcode.com/problems/sales-person/) | [Link](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Easy/607.Sales-Person.sql) | 
 | 20 | [608. Tree Node](https://leetcode.com/problems/tree-node/) | [Link](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Medium/608.Tree-Node.sql) | 
 | 21 | [620. Not Boring Movies](https://leetcode.com/problems/not-boring-movies/) | [Link](https://github.com/qanhnn12/SQL-Leetcode-Challenge-Solutions/blob/main/Not-Boring-Movies.sql) |