public class Solution {
public String reverseString(String s) {
if(s == null || s.length() < 2) return s;
int i = 0;
int j = s.length() - 1;
char[] str = s.toCharArray();
while (i < j) {
char temp = str[i];
str[i] = str[j];
str[j] = temp;
i++;
j--;
}
return new String(str);
}
}