541. Reverse String II

Given a string s and an integer k, reverse the first k characters for every 2k characters counting from the start of the string.

If there are fewer 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 leave the other as original.

Example 1:

Input: s = "abcdefg", k = 2
Output: "bacdfeg"

Example 2:

Input: s = "abcd", k = 2
Output: "bacd"

class Solution {
public:
    string reverseStr(string s, int k) {
        for(int i = 0;i < s.size();i = i + 2 * k)
            if(i +  k < s.size())
                reverse(s.begin() + i,s.begin() + i + k);
            else
                reverse(s.begin() + i,s.end());
        return s;
    }
};