add note

keineahnung2345 · Apr 18, 2022 · ceee6ea · ceee6ea
1 parent 6d6eb96
commit ceee6ea
Showing 1 changed file with 5 additions and 0 deletions.
diff --git a/18. 4Sum.md b/18. 4Sum.md
@@ -1,8 +1,13 @@
 # 18. 4Sum
 
+[leetcode - 18. 4Sum](https://leetcode.com/problems/4sum/)
+
 Runtime: 28 ms, faster than 78.17% of C++ online submissions for 4Sum.
 
 Memory Usage: 8.5 MB, less than 100.00% of C++ online submissions for 4Sum.
+
+Just wrap 3Sum problem with one more outer loop.
+
 ```cpp
 class Solution {
 public: