beats 80% runtime (stringbuilder solution)
IntuitionApproachComplexity
Time complexity:

Space complexity:
Code
# Intuition
<!-- Describe your first thoughts on how to solve this problem. -->

# Approach
<!-- Describe your approach to solving the problem. -->

# Complexity
- Time complexity:
<!-- Add your time complexity here, e.g. $$O(n)$$ -->

- Space complexity:
<!-- Add your space complexity here, e.g. $$O(n)$$ -->

# Code
```java []
class Solution {
    public boolean isFascinating(int n) {
        StringBuilder sb = new StringBuilder();
        sb.append(n);
        sb.append(n * 2);
        sb.append(n * 3);

        Set<Character> set = new HashSet<>();
        for (char c = '1'; c <= '9'; c++) set.add(c);

        for (char c : sb.toString().toCharArray()){
            if (!set.remove(c)) return false;
        }

        return set.size() == 0;
    }
}
```
['Java']