Update 076_minimum_window_substring.md

Author: Joseph Luce

leetcode/hard/076_minimum_window_substring.md

@@ -88,10 +88,10 @@ from collections import Counter
 
 class Solution:
     def minWindow(self, s: str, t: str) -> str:
-        char_counter = MinCharacterCounter(t)
+        char_counter = CharacterCounter(t)
         str_builder, min_substr, found = '', s, False
         for right_ch in s:
-            char_counter.increment(right_ch)
+            char_counter += right_ch
             str_builder += right_ch
             if char_counter.is_valid:
                 for left_ch in str_builder:
@@ -101,25 +101,27 @@ class Solution:
                             min_substr = str_builder
                     else:
                         break
-                    char_counter.decrement(left_ch)
+                    char_counter -= left_ch
                     str_builder = str_builder[1:]
         return min_substr if found else ''
         
-class MinCharacterCounter:
+class CharacterCounter:
     def __init__(self, source_str):
         self._ch_to_n_counts = defaultdict(int)
         self._source_counts = Counter(source_str)
         self._n_valid_chars = 0
 
-    def increment(self, char):
+    def __iadd__(self, char):
         self._ch_to_n_counts[char] += 1
         if char in self._source_counts and self._ch_to_n_counts[char] == self._source_counts[char]:
             self._n_valid_chars += 1
+        return self
         
-    def decrement(self, char):
+    def __isub__(self, char):
         self._ch_to_n_counts[char] -= 1
         if char in self._source_counts and self._ch_to_n_counts[char] == self._source_counts[char]-1:
             self._n_valid_chars -= 1
+        return self
     
     @property
     def is_valid(self):