Fix binary search to return first occurrence

Author: Aniket Kumar Singh

searches/binary_search.py

@@ -178,40 +178,28 @@ def insort_right(
 
 
 def binary_search(sorted_collection: list[int], item: int) -> int:
-    """Pure implementation of a binary search algorithm in Python
-
-    Be careful collection must be ascending sorted otherwise, the result will be
-    unpredictable
-
-    :param sorted_collection: some ascending sorted collection with comparable items
-    :param item: item value to search
-    :return: index of the found item or -1 if the item is not found
-
-    Examples:
-    >>> binary_search([0, 5, 7, 10, 15], 0)
-    0
-    >>> binary_search([0, 5, 7, 10, 15], 15)
-    4
-    >>> binary_search([0, 5, 7, 10, 15], 5)
-    1
-    >>> binary_search([0, 5, 7, 10, 15], 6)
-    -1
-    """
     if any(a > b for a, b in pairwise(sorted_collection)):
         raise ValueError("sorted_collection must be sorted in ascending order")
+
     left = 0
     right = len(sorted_collection) - 1
+    result = -1
 
     while left <= right:
         midpoint = left + (right - left) // 2
         current_item = sorted_collection[midpoint]
+
         if current_item == item:
-            return midpoint
+            result = midpoint
+            right = midpoint - 1
+
         elif item < current_item:
             right = midpoint - 1
+
         else:
             left = midpoint + 1
-    return -1
+
+    return result
 
 
 def binary_search_std_lib(sorted_collection: list[int], item: int) -> int: