Write a function that takes a string as input and returns the string reversed.

Example:
Given s = "hello", return "olleh".

class Solution {
    public String reverseString(String s) {
        if (s == null || s.length() <= 1) return s;

        char[] cArray = s.toCharArray();
        int start = 0, end = cArray.length - 1;
        while (start < end){
            char temp = cArray[start];
            cArray[start] = cArray[end];
            cArray[end] = temp;

            start++;
            end--;
        }

        return new String(cArray);
    }
}