Update find-the-duplicate-number.cpp

Author: kamyu104

C++/find-the-duplicate-number.cpp

@@ -1,7 +1,7 @@
 // Time: O(n)
 // Space: O(1)
 
-// Two pointers method, reference: http://keithschwarz.com/interesting/code/?dir=find-duplicate
+// Two pointers method, same as Linked List Cycle II
 class Solution {
 public:
  int findDuplicate(vector<int>& nums) {