leetcode Reverse String II 反转字符串

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]
题意：反转字符串s中下标为2k的倍数位置开始的长度为k的字符串
思路：一层循环找位置，一层循环反转字符串

class Solution {public:    string reverseStr(string s, int k) {        for (int left = 0; left <s.size(); left += 2 * k) {            for (int i = left, j = min(left + k - 1, (int)s.size() - 1); i < j; ++i, --j) {                swap(s[i], s[j]);            }        }        return s;    }};