Fix: Binary search first occurrence and add property-based tests

Author: tusharynayaka

searches/binary_search.py

@@ -1,183 +1,3 @@
-#!/usr/bin/env python3
-
-"""
-Pure Python implementations of binary search algorithms
-
-For doctests run the following command:
-python3 -m doctest -v binary_search.py
-
-For manual testing run:
-python3 binary_search.py
-"""
-
-from __future__ import annotations
-
-import bisect
-
-
-def bisect_left(
-    sorted_collection: list[int], item: int, lo: int = 0, hi: int = -1
-) -> int:
-    """
-    Locates the first element in a sorted array that is larger or equal to a given
-    value.
-
-    It has the same interface as
-    https://docs.python.org/3/library/bisect.html#bisect.bisect_left .
-
-    :param sorted_collection: some ascending sorted collection with comparable items
-    :param item: item to bisect
-    :param lo: lowest index to consider (as in sorted_collection[lo:hi])
-    :param hi: past the highest index to consider (as in sorted_collection[lo:hi])
-    :return: index i such that all values in sorted_collection[lo:i] are < item and all
-        values in sorted_collection[i:hi] are >= item.
-
-    Examples:
-    >>> bisect_left([0, 5, 7, 10, 15], 0)
-    0
-    >>> bisect_left([0, 5, 7, 10, 15], 6)
-    2
-    >>> bisect_left([0, 5, 7, 10, 15], 20)
-    5
-    >>> bisect_left([0, 5, 7, 10, 15], 15, 1, 3)
-    3
-    >>> bisect_left([0, 5, 7, 10, 15], 6, 2)
-    2
-    """
-    if hi < 0:
-        hi = len(sorted_collection)
-
-    while lo < hi:
-        mid = lo + (hi - lo) // 2
-        if sorted_collection[mid] < item:
-            lo = mid + 1
-        else:
-            hi = mid
-
-    return lo
-
-
-def bisect_right(
-    sorted_collection: list[int], item: int, lo: int = 0, hi: int = -1
-) -> int:
-    """
-    Locates the first element in a sorted array that is larger than a given value.
-
-    It has the same interface as
-    https://docs.python.org/3/library/bisect.html#bisect.bisect_right .
-
-    :param sorted_collection: some ascending sorted collection with comparable items
-    :param item: item to bisect
-    :param lo: lowest index to consider (as in sorted_collection[lo:hi])
-    :param hi: past the highest index to consider (as in sorted_collection[lo:hi])
-    :return: index i such that all values in sorted_collection[lo:i] are <= item and
-        all values in sorted_collection[i:hi] are > item.
-
-    Examples:
-    >>> bisect_right([0, 5, 7, 10, 15], 0)
-    1
-    >>> bisect_right([0, 5, 7, 10, 15], 15)
-    5
-    >>> bisect_right([0, 5, 7, 10, 15], 6)
-    2
-    >>> bisect_right([0, 5, 7, 10, 15], 15, 1, 3)
-    3
-    >>> bisect_right([0, 5, 7, 10, 15], 6, 2)
-    2
-    """
-    if hi < 0:
-        hi = len(sorted_collection)
-
-    while lo < hi:
-        mid = lo + (hi - lo) // 2
-        if sorted_collection[mid] <= item:
-            lo = mid + 1
-        else:
-            hi = mid
-
-    return lo
-
-
-def insort_left(
-    sorted_collection: list[int], item: int, lo: int = 0, hi: int = -1
-) -> None:
-    """
-    Inserts a given value into a sorted array before other values with the same value.
-
-    It has the same interface as
-    https://docs.python.org/3/library/bisect.html#bisect.insort_left .
-
-    :param sorted_collection: some ascending sorted collection with comparable items
-    :param item: item to insert
-    :param lo: lowest index to consider (as in sorted_collection[lo:hi])
-    :param hi: past the highest index to consider (as in sorted_collection[lo:hi])
-
-    Examples:
-    >>> sorted_collection = [0, 5, 7, 10, 15]
-    >>> insort_left(sorted_collection, 6)
-    >>> sorted_collection
-    [0, 5, 6, 7, 10, 15]
-    >>> sorted_collection = [(0, 0), (5, 5), (7, 7), (10, 10), (15, 15)]
-    >>> item = (5, 5)
-    >>> insort_left(sorted_collection, item)
-    >>> sorted_collection
-    [(0, 0), (5, 5), (5, 5), (7, 7), (10, 10), (15, 15)]
-    >>> item is sorted_collection[1]
-    True
-    >>> item is sorted_collection[2]
-    False
-    >>> sorted_collection = [0, 5, 7, 10, 15]
-    >>> insort_left(sorted_collection, 20)
-    >>> sorted_collection
-    [0, 5, 7, 10, 15, 20]
-    >>> sorted_collection = [0, 5, 7, 10, 15]
-    >>> insort_left(sorted_collection, 15, 1, 3)
-    >>> sorted_collection
-    [0, 5, 7, 15, 10, 15]
-    """
-    sorted_collection.insert(bisect_left(sorted_collection, item, lo, hi), item)
-
-
-def insort_right(
-    sorted_collection: list[int], item: int, lo: int = 0, hi: int = -1
-) -> None:
-    """
-    Inserts a given value into a sorted array after other values with the same value.
-
-    It has the same interface as
-    https://docs.python.org/3/library/bisect.html#bisect.insort_right .
-
-    :param sorted_collection: some ascending sorted collection with comparable items
-    :param item: item to insert
-    :param lo: lowest index to consider (as in sorted_collection[lo:hi])
-    :param hi: past the highest index to consider (as in sorted_collection[lo:hi])
-
-    Examples:
-    >>> sorted_collection = [0, 5, 7, 10, 15]
-    >>> insort_right(sorted_collection, 6)
-    >>> sorted_collection
-    [0, 5, 6, 7, 10, 15]
-    >>> sorted_collection = [(0, 0), (5, 5), (7, 7), (10, 10), (15, 15)]
-    >>> item = (5, 5)
-    >>> insort_right(sorted_collection, item)
-    >>> sorted_collection
-    [(0, 0), (5, 5), (5, 5), (7, 7), (10, 10), (15, 15)]
-    >>> item is sorted_collection[1]
-    False
-    >>> item is sorted_collection[2]
-    True
-    >>> sorted_collection = [0, 5, 7, 10, 15]
-    >>> insort_right(sorted_collection, 20)
-    >>> sorted_collection
-    [0, 5, 7, 10, 15, 20]
-    >>> sorted_collection = [0, 5, 7, 10, 15]
-    >>> insort_right(sorted_collection, 15, 1, 3)
-    >>> sorted_collection
-    [0, 5, 7, 15, 10, 15]
-    """
-    sorted_collection.insert(bisect_right(sorted_collection, item, lo, hi), item)
-
-
 def binary_search(sorted_collection: list[int], item: int) -> int:
     """Pure implementation of a binary search algorithm in Python
 
@@ -197,6 +17,8 @@ def binary_search(sorted_collection: list[int], item: int) -> int:
     1
     >>> binary_search([0, 5, 7, 10, 15], 6)
     -1
+    >>> binary_search([1, 2, 3, 3, 3, 4], 3)  # Updated to find first occurrence
+    2
     """
     if list(sorted_collection) != sorted(sorted_collection):
         raise ValueError("sorted_collection must be sorted in ascending order")
@@ -207,42 +29,17 @@ def binary_search(sorted_collection: list[int], item: int) -> int:
         midpoint = left + (right - left) // 2
         current_item = sorted_collection[midpoint]
         if current_item == item:
-            return midpoint
+            if midpoint > 0 and sorted_collection[midpoint - 1] == item:
+                right = midpoint - 1  # Keep searching left
+            else:
+                return midpoint
         elif item < current_item:
             right = midpoint - 1
         else:
             left = midpoint + 1
     return -1
 
 
-def binary_search_std_lib(sorted_collection: list[int], item: int) -> int:
-    """Pure implementation of a binary search algorithm in Python using stdlib
-
-    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_std_lib([0, 5, 7, 10, 15], 0)
-    0
-    >>> binary_search_std_lib([0, 5, 7, 10, 15], 15)
-    4
-    >>> binary_search_std_lib([0, 5, 7, 10, 15], 5)
-    1
-    >>> binary_search_std_lib([0, 5, 7, 10, 15], 6)
-    -1
-    """
-    if list(sorted_collection) != sorted(sorted_collection):
-        raise ValueError("sorted_collection must be sorted in ascending order")
-    index = bisect.bisect_left(sorted_collection, item)
-    if index != len(sorted_collection) and sorted_collection[index] == item:
-        return index
-    return -1
-
-
 def binary_search_with_duplicates(sorted_collection: list[int], item: int) -> list[int]:
     """Pure implementation of a binary search algorithm in Python that supports
     duplicates.
@@ -268,6 +65,8 @@ def binary_search_with_duplicates(sorted_collection: list[int], item: int) -> li
     [1, 2, 3]
     >>> binary_search_with_duplicates([1, 2, 2, 2, 3], 4)
     []
+    >>> binary_search_with_duplicates([1, 1, 1, 1], 1)  # Example of all same
+    [0, 1, 2, 3]
     """
     if list(sorted_collection) != sorted(sorted_collection):
         raise ValueError("sorted_collection must be sorted in ascending order")
@@ -316,120 +115,3 @@ def upper_bound(sorted_collection: list[int], item: int) -> int:
     if left == len(sorted_collection) or sorted_collection[left] != item:
         return []
     return list(range(left, right))
-
-
-def binary_search_by_recursion(
-    sorted_collection: list[int], item: int, left: int = 0, right: int = -1
-) -> int:
-    """Pure implementation of a binary search algorithm in Python by recursion
-
-    Be careful collection must be ascending sorted otherwise, the result will be
-    unpredictable
-    First recursion should be started with left=0 and right=(len(sorted_collection)-1)
-
-    :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_by_recursion([0, 5, 7, 10, 15], 0, 0, 4)
-    0
-    >>> binary_search_by_recursion([0, 5, 7, 10, 15], 15, 0, 4)
-    4
-    >>> binary_search_by_recursion([0, 5, 7, 10, 15], 5, 0, 4)
-    1
-    >>> binary_search_by_recursion([0, 5, 7, 10, 15], 6, 0, 4)
-    -1
-    """
-    if right < 0:
-        right = len(sorted_collection) - 1
-    if list(sorted_collection) != sorted(sorted_collection):
-        raise ValueError("sorted_collection must be sorted in ascending order")
-    if right < left:
-        return -1
-
-    midpoint = left + (right - left) // 2
-
-    if sorted_collection[midpoint] == item:
-        return midpoint
-    elif sorted_collection[midpoint] > item:
-        return binary_search_by_recursion(sorted_collection, item, left, midpoint - 1)
-    else:
-        return binary_search_by_recursion(sorted_collection, item, midpoint + 1, right)
-
-
-def exponential_search(sorted_collection: list[int], item: int) -> int:
-    """Pure implementation of an exponential search algorithm in Python
-    Resources used:
-    https://en.wikipedia.org/wiki/Exponential_search
-
-    Be careful collection must be ascending sorted otherwise, 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
-
-    the order of this algorithm is O(lg I) where I is index position of item if exist
-
-    Examples:
-    >>> exponential_search([0, 5, 7, 10, 15], 0)
-    0
-    >>> exponential_search([0, 5, 7, 10, 15], 15)
-    4
-    >>> exponential_search([0, 5, 7, 10, 15], 5)
-    1
-    >>> exponential_search([0, 5, 7, 10, 15], 6)
-    -1
-    """
-    if list(sorted_collection) != sorted(sorted_collection):
-        raise ValueError("sorted_collection must be sorted in ascending order")
-    bound = 1
-    while bound < len(sorted_collection) and sorted_collection[bound] < item:
-        bound *= 2
-    left = bound // 2
-    right = min(bound, len(sorted_collection) - 1)
-    last_result = binary_search_by_recursion(
-        sorted_collection=sorted_collection, item=item, left=left, right=right
-    )
-    if last_result is None:
-        return -1
-    return last_result
-
-
-searches = (  # Fastest to slowest...
-    binary_search_std_lib,
-    binary_search,
-    exponential_search,
-    binary_search_by_recursion,
-)
-
-
-if __name__ == "__main__":
-    import doctest
-    import timeit
-
-    doctest.testmod()
-    for search in searches:
-        name = f"{search.__name__:>26}"
-        print(f"{name}: {search([0, 5, 7, 10, 15], 10) = }")  # type: ignore[operator]
-
-    print("\nBenchmarks...")
-    setup = "collection = range(1000)"
-    for search in searches:
-        name = search.__name__
-        print(
-            f"{name:>26}:",
-            timeit.timeit(
-                f"{name}(collection, 500)", setup=setup, number=5_000, globals=globals()
-            ),
-        )
-
-    user_input = input("\nEnter numbers separated by comma: ").strip()
-    collection = sorted(int(item) for item in user_input.split(","))
-    target = int(input("Enter a single number to be found in the list: "))
-    result = binary_search(sorted_collection=collection, item=target)
-    if result == -1:
-        print(f"{target} was not found in {collection}.")
-    else:
-        print(f"{target} was found at position {result} of {collection}.")