Problem URL: Find k length substrings with no repeated characters

We will use a sliding window to solve this problem. The window will be a substring of the input string. The window will be valid if it has no repeated characters. We will keep track of the number of valid windows.

class Solution:
    def numKLenSubstrNoRepeats(self, s: str, k: int) -> int:
        count = collections.defaultdict(int)
        i, res = 0, 0
        for j, ch in enumerate(s):
            count[ch] += 1
            while j-i+1 > k:
                count[s[i]] -= 1
                if count[s[i]] == 0:
                    del count[s[i]]
                i += 1
            if j-i+1 == k and len(count) == k:
                res += 1
        return res

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