翻转单词顺序列——剑指offer

利用翻转函数，先对整串反转，再用pp和p两个指针判断单词的位置进行逐个反转。
细节处理要考虑串前面的空格，串中连续的多个空格，串的最后一个单词。

string reverse(string str, int left, int right)
{
    if (left<0 || right > str.length() - 1) {
        return "";
    }
    while (left < right) {
        char tmp;
        tmp = str[left];
        str[left] = str[right];
        str[right] = tmp;
        left++;
        right--;
    }
    return str;
}
string ReverseSentence(string str) {
    int left = 0;
    int right = str.length() - 1;
    str = reverse(str, left, right);
    int p = 0, pp = 0;
    //去掉开头的空格
    while (str[p] != '\0'&& str[p] == ' ') {
        p++;
    }
    pp = p;
    while (p < str.length()) {
        p++;
        if (str[p] == ' ' || str[p]== '\0') {
            str = reverse(str, pp, p-1);
            while (str[p] != '\0'&& str[p] == ' ') {
                p++;
            }
            pp = p;
        }
    }
    return str;
}