class Solution {
public:
void reverseString(vector& s) {
static int i = 0;
int n = s.size();
if(i>=n/2){
return;
}
swap(s[i], s[n-i-1]);
i++;
reverseString(s);
}
};

//Input : ["H","a","n","n","a","h"]
//Output : ["H","a","n","n","a","h"]
//Expected : ["h","a","n","n","a","H"]