Concatenation solution
Approach:Concatenate the numbers:We use string interpolation ($"{n}{n * 2}{n * 3}") to create the concatenated string.
Check the length:
The concatenated string

Approach:

Concatenate the numbers:

We use string interpolation ($"{n}{n * 2}{n * 3}") to create the concatenated string.
Check the length:
The concatenated string must have a length of 9.
Check for '0':
The concatenated string must not contain the digit '0'.
Check for unique digits:
The concatenated string must contain all 9 unique digits (1 to 9).

Complexity:

Time Complexity: O(1). The operations are performed on a fixed number of digits.
Space Complexity: O(1). The concatenated string's size is fixed.

# Code
```csharp []
public class Solution {
    public bool IsFascinating(int n) {
        string concatenated = $"{n}{n * 2}{n * 3}"; 
        return concatenated.Length == 9 &&        
               !concatenated.Contains('0') &&     
               concatenated.Distinct().Count() == 9; 
    }
}

```
['Hash Table', 'Math', 'C#']