How do you solve Check if The Number is Fascinating on LeetCode?

Check if The Number is Fascinating (LeetCode #2729) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: The problem requires checking for unique digits, which can be efficiently managed using a set.

What is the brute force solution for Check if The Number is Fascinating?

The brute force approach for Check if The Number is Fascinating is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves concatenating the number n with 2 * n and 3 * n, then checking if the resulting string contains all digits from 1 to 9 exactly once. This is straightforward but can be inefficient if not handled properly. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Check if The Number is Fascinating?

Check if The Number is Fascinating uses the following concepts: Hash Table, Math. The recommended patterns to study are: Hash Map, Array.

What are the interview tips for Check if The Number is Fascinating?

Always clarify the constraints of the input before diving into the solution. Consider edge cases, such as numbers that might contain '0'. Explain your thought process clearly; it shows your understanding and can help guide your interviewer.

What are common mistakes when solving Check if The Number is Fascinating?

Not handling the case where '0' is present in the concatenated string. Forgetting to check the size of the set to ensure all digits are present.

#2729

Check if The Number is Fascinating

Easy

Hash TableMathHash MapArray

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

The optimal solution builds on the brute force approach but uses a set to track the digits. This avoids the need for sorting and allows for a more efficient check for uniqueness and completeness.

⚙️

Algorithm

3 steps

1Step 1: Calculate 2 * n and 3 * n.
2Step 2: Concatenate n, 2 * n, and 3 * n into a single string.
3Step 3: Use a set to track digits and ensure all digits from 1 to 9 are present without duplicates.

solution.py3 lines

1def is_fascinating(n):
2    concatenated = str(n) + str(2 * n) + str(3 * n)
3    return len(set(concatenated)) == 9 and '0' not in concatenated

ℹ

Complexity note: The time complexity is O(n) because we traverse the concatenated string once. The space complexity is O(n) due to the storage of unique digits in a set.

1The problem requires checking for unique digits, which can be efficiently managed using a set.
2Understanding the constraints (3-digit numbers) allows for simpler checks without worrying about larger inputs.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.