CS250 2023Fall HW3 Problem 4.1.6

cs250_2023fall_hw3_p4_1_6.py

"""
CS250 2023Fall HW3 Problem 4.1.6
Author: Jonah Y-M

Copyright: (CC BY-SA 4.0) Attribution-ShareAlike 4.0 International
"""
import sys

assert sys.version_info >= (3, 12), "Python 3.12+ required."

# --- setup ---

TEST_RANGE = 16

type natural = int

# --- the natual minus function ---

def minus(x: natural, y: natural) -> natural:
    """ x - y for natural numbers """
    assert x >= 0
    assert y >= 0
    
    if y > x:
        return 0

    if y > 0:
        x = minus(x - 1, y - 1)

    return x


# --- test ---

if __name__ == "__main__":
    res: dict[tuple[int, int], tuple[int, int]] = {
        (x, y): (
            x - y if x >= y else 0,  # python result for `minus(x, y)`
            minus(x, y),  # test target, my result for `minus(x, y)`
        )
        for x in range(TEST_RANGE)
        for y in range(TEST_RANGE)
    }

    for (x, y), (py_res, my_res) in res.items():
        print(f"minus({x}, {y}) = {my_res} (expected {py_res})")
        assert py_res == my_res
    else:
        print("All tests passed!")