chore: add Counter class

src/counter.py

@@ -0,0 +1,20 @@
+
+class Counter:
+  def __init__(self, val=0):
+    self.reset_on = val
+    self.val = val
+  
+  def __repr__(self):
+    return f"Counter: {self.val} [reset on {self.reset_on}]"
+  
+  def incr(self):
+    self.val += 1
+    return self.val
+
+  def decr(self):
+    self.val -= 1
+    return self.val
+
+  def reset(self):
+    self.val = self.reset_on
+    return self.val

src/main.py

@@ -2,6 +2,7 @@
 
 from strings import *
 from tree import *
+from counter import *
 
 def trees():
   t = build_tree((1, 
@@ -73,8 +74,30 @@ def trees():
   assert number_of_nodes(build_tree((0, (1, None, None), (2, None, None)))) == 3
   assert number_of_nodes(build_tree((0, (1, (3, None, None), None), (2, None, None)))) == 4
 
-def main():
+def counter():
+  c = Counter()
+  assert c.incr() == 1
+  assert c.decr() == 0
+  assert c.decr() == -1
+  assert c.reset() == 0
 
+  c = Counter(5)
+  c.incr()
+  c.incr()
+  c.incr()
+  assert c.val == 8
+  c.reset()
+  assert c.val == 5
+
+  c = Counter(-1)
+  assert c.val == -1
+  c.incr()
+  c.incr()
+  assert c.val == 1
+
+
+def main():
+  counter()
   pass
 
 if __name__ == "__main__":