from typing import Sequence, TypeVar


T = TypeVar("T", bound=str | float)


def missingValue(L: Sequence[T], M: Sequence[T]) -> T | None:
    """Return the missing value from one of the two sorted sequences."""
    if (not L) and M:
        return M[0]
    elif (not M) and L:
        return L[0]
    elif (not L) and (not M):
        return None
    L = sorted(L)
    M = sorted(M)
    larger = L if len(L) > len(M) else M
    smaller = L if len(L) < len(M) else M
    for i in range(len(larger)):
        a = larger[i]
        if i > (len(smaller) - 1):
            return a
        b = smaller[i]
        if a != b:
            return larger[i]
    return None


print("Testing missingValue()...", end="")
assert missingValue([1, 2, 3], [3, 1]) == 2
assert missingValue([1, 2, 3], [2, 1]) == 3
assert missingValue(["A", "B", "A", "C"], ["C", "A", "B"]) == "A"
assert missingValue(["A", "B", "A", "C"], ["A", "A", "B"]) == "C"
assert missingValue(["A", "B", "A", "C"], ["A", "C", "A"]) == "B"
assert missingValue([2, 2], [2]) == 2
assert missingValue([2, 3], [2]) == 3
assert missingValue([2, 3], [3]) == 2
assert missingValue(["amazing"], []) == "amazing"

# Make sure the function is non-mutating
L = [1, 2, 3]
M = [3, 1]
assert missingValue(L, M) == 2
assert L == [1, 2, 3]
assert M == [3, 1]
print("Passed!")