Fix binary search to handle duplicates correctly

Author: rahini

searches/binary_search_with_duplicates.py

@@ -1,18 +1,21 @@
-def binary_search_first_occurrence(arr, target):
+def binary_search_first_occurrence(arr: list[int], target: int) -> int:
+    """
+    Return the index of the first occurrence of target in a sorted list.
+
+    >>> binary_search_first_occurrence([1, 2, 4, 4, 4, 5], 4)
+    2
+    >>> binary_search_first_occurrence([1, 2, 3], 5)
+    -1
+    """
     left, right = 0, len(arr) - 1
     result = -1
     while left <= right:
         mid = (left + right) // 2
         if arr[mid] == target:
             result = mid
-            right = mid - 1  # keep searching left
+            right = mid - 1
         elif arr[mid] < target:
             left = mid + 1
         else:
             right = mid - 1
     return result
-
-if __name__ == "__main__":
-    arr = [1, 2, 4, 4, 4, 5, 6]
-    target = 4
-    print(binary_search_first_occurrence(arr, target))  # Expected output: 2