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LeetCode - 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]
class Solution {
    public String reverseStr(String s, int k) {
        StringBuilder ret = new StringBuilder();   
        
if (s.length() <= k) { for (int i=0; i<s.length(); i++) ret.append(s.charAt(s.length()-i-1)); return ret.toString(); } int kc = s.length() / k; if ((s.length() % k) != 0) kc ++; for (int ki=0; ki<kc; ki++) {
if ((ki&1)==0) for (int i=Math.min((ki+1)*k-1,s.length()-1); i>=ki*k; i--) ret.append(s.charAt(i)); else for (int i=ki*k; i<(ki+1)*k&&i<s.length(); i++) ret.append(s.charAt(i)); } return ret.toString(); } }

LeetCode - 541. Reverse String II