class Solution {
    
    // 문자열 뒤집기 
    // T: O(n)
    // S: O(1)
    public void reverseString(char[] s) {
        int left = 0, right = s.length - 1;
        while (left < right) {
            swap(s, left++, right--);
        }
    }
    
    public void swap(char[] s, int left, int right) {
        char temp = s[left];
        s[left] = s[right];
        s[right] = temp; 
    }
}