Create multiplexer.py (#11064)

* Create multiplexer.py

* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* Doctests should show how the algorithm fails

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

boolean_algebra/multiplexer.py

@@ -0,0 +1,42 @@
+def mux(input0: int, input1: int, select: int) -> int:
+    """
+    Implement a 2-to-1 Multiplexer.
+
+    :param input0: The first input value (0 or 1).
+    :param input1: The second input value (0 or 1).
+    :param select: The select signal (0 or 1) to choose between input0 and input1.
+    :return: The output based on the select signal.  input1 if select else input0.
+
+    https://www.electrically4u.com/solved-problems-on-multiplexer
+    https://en.wikipedia.org/wiki/Multiplexer
+
+    >>> mux(0, 1, 0)
+    0
+    >>> mux(0, 1, 1)
+    1
+    >>> mux(1, 0, 0)
+    1
+    >>> mux(1, 0, 1)
+    0
+    >>> mux(2, 1, 0)
+    Traceback (most recent call last):
+        ...
+    ValueError: Inputs and select signal must be 0 or 1
+    >>> mux(0, -1, 0)
+    Traceback (most recent call last):
+        ...
+    ValueError: Inputs and select signal must be 0 or 1
+    >>> mux(0, 1, 1.1)
+    Traceback (most recent call last):
+        ...
+    ValueError: Inputs and select signal must be 0 or 1
+    """
+    if all(i in (0, 1) for i in (input0, input1, select)):
+        return input1 if select else input0
+    raise ValueError("Inputs and select signal must be 0 or 1")
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()