Update tortoise_and_hare.md

ericmiranda7 · web-flow · commit f2f28eacb0df · 2025-01-10T07:05:26.000+05:30
the happy number problem can be solved using a hashset, but it can also be solved in constant space using floyd's algo
diff --git a/src/others/tortoise_and_hare.md b/src/others/tortoise_and_hare.md
@@ -110,5 +110,6 @@ And since we let the slow pointer start at the start of the linked list, after $
 
 # Problems:
 - [Linked List Cycle (EASY)](https://leetcode.com/problems/linked-list-cycle/)
+- [Happy Number (Easy)](https://leetcode.com/problems/happy-number/)
 - [Find the Duplicate Number (Medium)](https://leetcode.com/problems/find-the-duplicate-number/)
 
