Created bianry_to_excessthree.py (#13831)

* Create bianry_to_excessthree.py

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* Fix filename typos in binary to excess-3 conversion

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

Author: 3 people

conversions/binary_to_excess3.py

@@ -0,0 +1,34 @@
+def binary_to_excess3(binary_str: str) -> str:
+    """
+    Convert a binary number (as a string) to its Excess-3 code.
+    https://en.wikipedia.org/wiki/Excess-3
+
+    Args:
+        binary_str (str): Binary number as a string (e.g., "1010").
+
+    Returns:
+        str: Excess-3 code as a binary string.
+
+    Example:
+        >>> binary_to_excess3("1010")
+        '1101'
+    """
+    # Convert binary to decimal
+    decimal_value = int(binary_str, 2)
+
+    # Add 3 (Excess-3 encoding)
+    excess3_value = decimal_value + 3
+
+    # Convert back to 4-bit binary
+    excess3_binary = format(excess3_value, "04b")
+
+    return excess3_binary
+
+
+if __name__ == "__main__":
+    from dostest import testmod
+
+    testmod()
+    binary_input = input("Enter a 4-bit binary number: ")
+    excess3_output = binary_to_excess3(binary_input)
+    print(f"Excess-3 code of {binary_input} is: {excess3_output}")