541. Reverse String II

1. Description

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.

2. Example

Example 1:
Input: s = “abcdefg”, k = 2
Output: “bacdfeg”

3. Constraints

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

4. Solutions

My Accepted Solution

n = m_str.size()
Time complexity: O(n)
Space complexity: O(n)

class Solution 
{
public:
    // string reverseStr(string s, int k)
    string reverseStr(string &m_str, int k) 
    {
        int index = 0;
        while(index < m_str.size())
        {
            reverse(m_str.begin() + index, m_str.begin() + min(index + k, (int)m_str.size()));
            
            index += 2 * k;
        }
        
        return m_str;
    }
};