Update valid-square.py

Author: kamyu104

Python/valid-square.py

@@ -28,7 +28,7 @@ def validSquare(self, p1, p2, p3, p4):
         def dist(p1, p2):
             return (p1[0] - p2[0]) ** 2 + (p1[1] - p2[1]) ** 2
 
-        counter = collections.Counter([dist(p1, p2), dist(p1, p3),\
-                                       dist(p1, p4), dist(p2, p3),\
-                                       dist(p2, p4), dist(p3, p4)])
-        return counter[0] == 0 and len(counter) == 2
+        lookup = set([dist(p1, p2), dist(p1, p3),\
+                      dist(p1, p4), dist(p2, p3),\
+                      dist(p2, p4), dist(p3, p4)])
+        return 0 not in lookup and len(lookup) == 2