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 = 2 Output: "bacdfeg"

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

Solution: Using flag

We use flag to mark whether we should reverse the string.

void reverse(string& text, int lhs, int rhs) {
    while (lhs < rhs) {
        char temp = text[lhs];
        text[lhs++] = text[rhs];
        text[rhs--] = temp;
    }
} 

string reverseStr(string s, int k) {
    bool flip = true;
    for (int ix = 0; ix < s.length(); ix += k) {
        if (flip) {
          reverse(s, ix, min((int)s.length(), ix + k) - 1);
        }

        flip = !flip;
    }

    return s;
}