# 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

| Item | Meaning |
|---|---|
| Input | Integer `n` |
| Output | `true` if rotating 180° gives a different valid number |

Function shape:

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

## Examples

Example 1:

```python
n = 6
```

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

Example 2:

```python
n = 89
```

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

Example 3:

```python
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

```python
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

```python
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()
```

| Test | Expected | Why |
|---|---:|---|
| `6` | `True` | Rotates to `9` |
| `89` | `True` | Rotates to `68` |
| `11` | `False` | Rotates to `11` (same) |
| `25` | `False` | `2` is not a valid rotation digit |