https://leetcode.com/problems/reverse-string/

class Solution {
public:
  void reverseString(vector<char> &s) {
    int n = s.size();

    for (int i = 0; i < n / 2; i++) {
      char tmp = s[i];
      s[i] = s[n - i - 1];
      s[n - i - 1] = tmp;
    }
  }
};