541. Reverse String II

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LeetCode

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Problem

Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string.

If there are fewer 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 leave the other as original.

Example 1:

Input: s = "abcdefg", k = 2
Output: "bacdfeg"

Example 2:

Input: s = "abcd", k = 2
Output: "bacd"

Code

class Solution {
    public String reverseStr(String s, int k) {
        char[] arr = s.toCharArray();
        int len = s.length();
        
        int i = 0;
        while(i < len) {
            int j = Math.min(i + k - 1, len - 1);
            
            swap(arr, i, j);
            
            i += 2 * k;
        }
        
        return String.valueOf(arr);
    }
    
    private void swap(char[] arr, int left, int right) {
        while (left < right) {
            char temp = arr[left];
            arr[left] = arr[right];
            arr[right] = temp;
            
            left++;
            right--;
        }
    }
}