[LeetCode] Problem 541 - Reverse String II

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Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are less than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.

Example

Input: s = “abcdefg”, k = 2

Output: “bacdfeg”

Restrictions

  1. The string consists of lower English letters only.
  2. Length of the given string and k will in the range [1, 10000]

Code

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public String reverseStr(String s, int k) {
    char[] str = s.toCharArray();

    for (int i = 0; i < s.length(); i += 2 * k) {
        int start = i;
        int end = Math.min(i + k - 1, s.length() - 1);

        while (start < end) {
            char temp = str[end];
            str[end] = str[start];
            str[start] = temp;

            start++;
            end--;
        }
    }

    return String.valueOf(str);
}