add 2001

Author: fishercoder1534

README.md

@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ ★
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                  
 |-----|----------------|---------------|--------|-------------|-------------
+|2001|[Number of Pairs of Interchangeable Rectangles](https://leetcode.com/problems/number-of-pairs-of-interchangeable-rectangles/)|[Python3](../master/python3/_2001.py) ||Medium||
 |2000|[Reverse Prefix of Word](https://leetcode.com/problems/reverse-prefix-of-word/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_2000.java) ||Easy||
 |1996|[The Number of Weak Characters in the Game](https://leetcode.com/problems/the-number-of-weak-characters-in-the-game/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1996.java) ||Medium||
 |1995|[Count Special Quadruplets](https://leetcode.com/problems/count-special-quadruplets/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1995.java) ||Easy||

python3/2001.py

@@ -0,0 +1,13 @@
+from fractions import *
+from collections import Counter
+
+class Solution:
+    #credit: https://leetcode-cn.com/u/lucifer1004/
+    def interchangeableRectangles(self, rectangles: List[List[int]]) -> int:
+        cnt = Counter()
+        for w, h in rectangles:
+            cnt[Fraction(w, h)] += 1
+        ans = 0
+        for value in cnt.values():
+            ans += value * (value - 1) // 2
+        return ans