Java Concise Solution
\npublic class Solution {\n    public String reverseStr(String s, int k) {\n        char[] arr = s.toCharArray();\n        int n = arr.length;\n        int i = 
```\npublic class Solution {\n    public String reverseStr(String s, int k) {\n        char[] arr = s.toCharArray();\n        int n = arr.length;\n        int i = 0;\n        while(i < n) {\n            int j = Math.min(i + k - 1, n - 1);\n            swap(arr, i, j);\n            i += 2 * k;\n        }\n        return String.valueOf(arr);\n    }\n    private void swap(char[] arr, int l, int r) {\n        while (l < r) {\n            char temp = arr[l];\n            arr[l++] = arr[r];\n            arr[r--] = temp;\n        }\n    }\n}\n```
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