text: static int fastio=[](){
      std::ios::sync_with_stdio(false);
      cin.tie(NULL);
      cout.tie(NULL);
      return 0;
  }();
  class Solution {
  public:
      void reverseString(vector<char>& s) {
          int i=0,j=s.size()-1;
          while(i<j){
              char t=s[i];
              s[i]=s[j];
              s[j]=t;
              ++i;
              --j;
          }
      }
  };
  