Python3 Simple Solution (6 lines)
Intuition\nThink of loop and iteration.\n Describe your first thoughts on how to solve this problem. \n\n# Approach\nIncremenet a variable by concatenating the 
# Intuition\nThink of loop and iteration.\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\nIncremenet a variable by concatenating the substring of string.\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity: O(n)\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity: O(1)\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\nclass Solution:\n    def reverseStr(self, s: str, k: int) -> str:\n        i = 0\n        S = \'\'\n        while i < len(s):\n            S += s[i:i + k][::-1]\n            S += s[i + k:i + k + k]\n            i += k + k\n        return S\n```
['Python3']