Add similarity snippet

snippets/similarity.md

@@ -0,0 +1,17 @@
+---
+title: similarity
+tags: list,beginner
+---
+
+Returns a list of elements that exist in both lists.
+
+Use list comprehension on `a` to only keep values contained in both lists.
+
+```py
+def similarity(a, b):
+  return [item for item in a if item in b]
+```
+
+```py
+similarity([1, 2, 3], [1, 2, 4]) # [1, 2]
+```