LeetCode 1056: Confusing Number

Problem Restatement

A confusing number is a number that when rotated 180 degrees becomes a different valid number.

The valid rotations are: 0 → 0, 1 → 1, 6 → 9, 8 → 8, 9 → 6.

Digits 2, 3, 4, 5, 7 are invalid — rotating them produces no valid digit.

We are given a number n. Return true if it is a confusing number.

Input and Output

Function shape:

def confusingNumber(n: int) -> bool:
    ...

Examples

Example 1:

n = 6

Rotating 6 gives 9. Valid and different. Answer: True.

Example 2:

n = 89

Rotating gives 68. Valid and different. Answer: True.

Example 3:

n = 11

Rotating 11 gives 11. Same number. Answer: False.

Key Insight

Build the rotated number by reversing the digits and applying the rotation map. If any digit is invalid, return False. If the rotated number differs from the original, return True.

Edge Cases

• Check the minimum input size allowed by the constraints.
• Verify duplicate values or tie cases if the input can contain them.
• Keep the return value aligned with the exact failure case in the statement.

Common Pitfalls

• Do not optimize away the invariant; the code should still make it clear what condition is being maintained.
• Prefer problem-specific names over one-letter variables once the logic becomes stateful.

Implementation

class Solution:
    def confusingNumber(self, n: int) -> bool:
        rotate = {0: 0, 1: 1, 6: 9, 8: 8, 9: 6}
        original = n
        rotated = 0

        while n > 0:
            digit = n % 10
            if digit not in rotate:
                return False
            rotated = rotated * 10 + rotate[digit]
            n //= 10

        return rotated != original

Testing

def run_tests():
    s = Solution()

    assert s.confusingNumber(6) == True
    assert s.confusingNumber(89) == True
    assert s.confusingNumber(11) == False
    assert s.confusingNumber(25) == False

    print("all tests passed")

run_tests()