Solution541.java

import java.util.Arrays;

/**
 * Created by slade on 2019/12/26.
 */
public class Solution541 {
 public String reverseStr(String s, int k) {
 if (s.length() > 2 * k) {
 return reverseSingle(s.substring(0, 2 * k), k) + reverseStr(s.substring(2 * k), k);
 } else {
 return reverseSingle(s, k);
 }

 }

 public String reverseSingle(String s, int k) {
 if (s.length() >= k) {
 String s1 = new StringBuffer(s.substring(0, k)).reverse().toString();
 String s2 = s.substring(k).toString();
 return s1 + s2;
 } else {
 String s1 = new StringBuffer(s).reverse().toString();
 return s1;
 }
 }

 public static void main(String[] args) {
 Solution541 solution541 = new Solution541();
 System.out.println(solution541.reverseStr("abcdefg", 2));
 }
}