Problem URL: Number of substrings containing all three characters

We can use a sliding window to solve the problem. We will use a variable count to store the number of substrings containing all three characters. Then we will iterate over the string and update count accordingly. Finally, we will return count.

class Solution:
    def numberOfSubstrings(self, s: str) -> int:
        res = i = 0
        count = {c: 0 for c in 'abc'}
        for j in range(len(s)):
            count[s[j]] += 1
            while all(count.values()):
                count[s[i]] -= 1
                i += 1
            res += i
        return res

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