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 = 2Output: "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]

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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;    }};