python Solution || Sliding window
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        cnt =0\n        left =0\n        mp={}\n        for right in range(len(s)):\n            mp[s[right]]=mp.get(s[right],0)+1\n            while mp[s[right]]>=k:\n                mp[s[left]]-=1\n                cnt += len(s)-right\n                left+=1\n        return cnt\n        \n```
['Python3']