Question

How to check if every digit in a number appears only once in Python

Answer 1

# n % 10 extracts the last digit.
# 1 << digit creates a bitmask for that digit.
# mask & bit checks whether the bit for this digit is already set.
# Mark the digit as seen: mask |= bit; This sets the bit for the current digit.

def all_digits_unique(n: int) -> bool:
    mask = 0

    while n > 0:
        digit = n % 10
        bit = 1 << digit

        if mask & bit:
            return False  # digit already seen
        mask |= bit

        n //= 10

    return True


if __name__ == "__main__":
    n = 123456
    print("Unique" if all_digits_unique(n) else "Not unique")

    n = 123452
    print("Unique" if all_digits_unique(n) else "Not unique")
             


'''
run:

Unique
Not unique

'''

 

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