看到同事出去的面试题，将“hello world” 转换成 “ world hello"还要考虑空间复杂度

然后就随便写写，主要是c思路，用c语言估计可以更简洁，也不知道是不是面试官想要的答案

String s = "hello world 123 321";

Field f = s.getClass().getDeclaredField("value");

f.setAccessible(true);

char[] chrs = (char[]) f.get(s);

char temp;

for (int i = 0; i < chrs.length / 2; i++) {

          temp = chrs[i];

          chrs[i] = chrs[chrs.length - i - 1];

          chrs[chrs.length - i - 1] = temp;

}

System.out.println(s);

int lastIndex = 0;

for (int i = 0; i < chrs.length; i++) {

         if (chrs[i] == ' ' || i == chrs.length - 1) {

                     if (i == chrs.length - 1)

                     i = i + 1;

                     for (int j = lastIndex; j < lastIndex + (i - lastIndex) / 2; j++) {

                                temp = chrs[j];

                                chrs[j] = chrs[i - j - 1 + lastIndex];

                                 chrs[i - j - 1 + lastIndex] = temp;

                        }

              lastIndex = i + 1;

            }

}

System.out.println(s);