1876. Substrings of Size Three with Distinct Characters

Problem

Difficulty: Easy
Tags: Mid Level, Hash Table, String, Sliding Window, Counting, Biweekly Contest 53

Intuition

This question is much easier than previous question. I could do check all the possible substrings of length 3, and it wasn’t that slow.

if 3 gets bigger to like 10 or 100, I might do with different method, but for this problem, checking every combination was fine.

Approach

let i be idex of first element of substring with length 3, and check every possible substring by increasing i by 1.

Solution

class Solution:
    def countGoodSubstrings(self, s: str) -> int:
        if len(s) < 3:
            return 0

        count = 0
        i = 0
        while i+3 <= len(s):
            if not(s[i] == s[i+1] or s[i] == s[i+2] or s[i+1] == s[i+2]):
                count += 1
            i += 1

        return count

Complexity

Time: $O(n)$
Space: $O(1)$

Thoughts

This one was easy.