解题思路

双指针

 public void reverseString(char[] s) {
      if(s == null || s.length < 2)
         return;
      int left = -1;
      int right = s.length;
      while(++left < --right){
         char c = s[left];
         s[left] = s[right];
         s[right] = c;
      }
      return;
    }