sliding window technique
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```python3 []\nclass Solution:\n    def numberOfSubstrings(self, s: str, k: int) -> int:\n        l = 0\n        res = 0\n        d = defaultdict(int)\n        maxvalues = 0\n        for l in range(len(s)):\n            d.clear()\n            maxvalues = 0\n            for r in range(l, len(s)):\n                d[s[r]] += 1\n                maxvalues = max(maxvalues, d[s[r]])\n                if maxvalues >= k:\n                    res += 1\n        return res\n                \n```
['Python3']