Fix Boyer-Moore bug bad character shift logic

Author: Divyanshu-hash

strings/boyer_moore_search.py

@@ -13,9 +13,12 @@
 
 If there is no mismatch then the pattern matches with text block.
 
-Time Complexity : O(n/m)
+Time Complexity : O(n/m) average case with bad character heuristic
     n=length of main string
     m=length of pattern string
+
+Note: The bad character shift requires a while loop so positions are
+    actually skipped. A for loop ignores loop-variable reassignment.
 """
 
 
@@ -78,23 +81,33 @@ def mismatch_in_text(self, current_pos: int) -> int:
 
     def bad_character_heuristic(self) -> list[int]:
         """
-        Finds the positions of the pattern location.
+        Finds the positions of the pattern in text using the bad character
+        heuristic. A while loop is used so the shift actually skips
+        positions, achieving O(n/m) average performance instead of the
+        O(nm) brute-force that a for loop would produce.
 
         >>> bms = BoyerMooreSearch(text="ABAABA", pattern="AB")
         >>> bms.bad_character_heuristic()
         [0, 3]
+        >>> bms2 = BoyerMooreSearch(text="AAAAAA", pattern="AA")
+        >>> bms2.bad_character_heuristic()
+        [0, 1, 2, 3, 4]
+        >>> bms3 = BoyerMooreSearch(text="ABCDEF", pattern="XY")
+        >>> bms3.bad_character_heuristic()
+        []
         """
 
         positions = []
-        for i in range(self.textLen - self.patLen + 1):
+        i = 0
+        while i <= self.textLen - self.patLen:
             mismatch_index = self.mismatch_in_text(i)
             if mismatch_index == -1:
                 positions.append(i)
+                i += 1
             else:
                 match_index = self.match_in_pattern(self.text[mismatch_index])
-                i = (
-                    mismatch_index - match_index
-                )  # shifting index lgtm [py/multiple-definition]
+                # Use max to prevent shifting backwards
+                i = max(i + 1, mismatch_index - match_index)
         return positions