//time:o(n)
//space:o(1)

class Solution {
    public void reverseString(char[] s) {
        if(s == null ||s.length == 0) return;
        int left = 0;
        int right = s.length- 1;
        while (left < right) {
            char temp = s[left];
            s[left++] = s[right];
            s[right--] = temp;
        
    }
    }
}