541. Reverse String II

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

Subscribe to see which companies asked this question.

Solution:

Tips:

Just reverse the code by group, and deal the last words less than k specifically.

Java Code:

public class Solution { public String reverseStr(String s, int k) { if (s == null || k < 2) { return s; } StringBuilder result = new StringBuilder(); int i = 0; int kCount = 0; while (i < s.length()) { int n = k; int beginIdx = kCount % 2 == 0 ? i + k - 1 : i; int step = kCount % 2 == 0 ? -1 : 1; if (i + k > s.length()) { break; } kCount++; i += k; while (n-- > 0) { result.append(s.charAt(beginIdx)); beginIdx += step; } } StringBuilder tailStr = new StringBuilder(s.substring(i, s.length())); if (kCount % 2 == 0) { result.append(tailStr.reverse()); } else { result.append(tailStr); } return new String(result); } }