[LeetCode]--344. Reverse String

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

Example:
Given s = “hello”, return “olleh”.

public String reverseString(String s) {
        char[] ss = s.toCharArray();
        int j = ss.length - 1, i = 0;
        char temp;
        while (i < j) {
            temp = ss[i];
            ss[i] = ss[j];
            ss[j] = temp;
            i++;
            j--;
        }
        return String.valueOf(ss);
    }

AC了，我想着用栈会不会更加快，没想到。。。

//超时了
    public String reverseString(String s) {
        Stack<Character> stack = new Stack<Character>();
        String str = "";
        for (int i = 0; i < s.length(); i++)
            stack.add(s.charAt(i));
        while(!stack.isEmpty())
            str += stack.pop();
        return str;
    }

这个不能AC