What is the brute force solution for Substrings of Size Three with Distinct Characters?

The brute force approach for Substrings of Size Three with Distinct Characters is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute-force approach involves generating all possible substrings of length three and checking if they contain distinct characters. This is straightforward but inefficient for larger strings. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Substrings of Size Three with Distinct Characters?

Substrings of Size Three with Distinct Characters uses the following concepts: Hash Table, String, Sliding Window, Counting. The recommended patterns to study are: Sliding Window, Hash Map.

What are the interview tips for Substrings of Size Three with Distinct Characters?

Explain your thought process clearly while coding. Consider edge cases, such as very short strings. Use descriptive variable names to enhance readability.

What are common mistakes when solving Substrings of Size Three with Distinct Characters?

Not checking all characters in the substring for distinctness. Confusing substrings with non-contiguous characters.

#1876

Substrings of Size Three with Distinct Characters

Easy

Hash TableStringSliding WindowCountingSliding WindowHash Map

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Approaches

Brute ForceOptimal

Complexity Comparison

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

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Intuition

Time O(n)Space O(1)

Using a sliding window approach allows us to efficiently check each substring of length three without needing to extract and check each substring separately. This reduces the time complexity significantly.

⚙️

Algorithm

5 steps

1Step 1: Initialize a counter to zero and a set to track distinct characters.
2Step 2: Loop through the string while maintaining a sliding window of size 3.
3Step 3: For each new character added to the window, check if it is distinct from the previous two characters.
4Step 4: If the window has three distinct characters, increment the counter.
5Step 5: Move the window one character to the right and repeat until the end of the string.

solution.py6 lines

1def countGoodSubstrings(s):
2    count = 0
3    for i in range(len(s) - 2):
4        if len(set(s[i:i+3])) == 3:
5            count += 1
6    return count

ℹ

Complexity note: The time complexity is O(n) since we only make a single pass through the string. The space complexity is O(1) as we are not using additional data structures that grow with input size.

1A substring is only good if all characters are distinct.
2Using a set can help quickly determine if characters are distinct.

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