翻转单词顺序

class Solution {
    public String reverseWords(String s) {
         String[] str = s.split(" ");
        reverse(str);
        int len = str.length;
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < len; i++) {
            sb.append(str[i]);
            if (i != len - 1){
                sb.append(" ");
            }
        }
        return sb.toString();
    }

    public void reverse(String[] str) {
        int len = str.length;
        int i = 0, j = len - 1;
        while (i < j) {
            String s = str[i];
            str[i++] = str[j];
            str[j--] = s;
        }
    }
}