翻转单词顺序列

题目描述

牛客最近来了一个新员工Fish，每天早晨总是会拿着一本英文杂志，写些句子在本子上。同事Cat对Fish写的内容颇感兴趣，有一天他向Fish借来翻看，但却读不懂它的意思。例如，“student. a am I”。后来才意识到，这家伙原来把句子单词的顺序翻转了，正确的句子应该是“I am a student.”。Cat对一一的翻转这些单词顺序可不在行，你能帮助他么？

解法

两步翻转，先翻转整个序列，然后在对单个单词进行翻转；

代码

     string ReverseSentence(string str) {
        if (str == "" || str.length() == 1) return str;
        int length = str.length()-1;
        reverseStr(&str, 0, length);
        char blank = ' ';
        int b=-1;
        for (int i = 0; i <= length; i++) {
            if (b == -1 && str[i] != blank) {
                b = i;
                continue;
            }
            if (b != -1 && (str[i] == blank|| i == length)) {
                if (str[i] == blank) {
                    reverseStr(&str, b, i - 1);
                    b = -1;
                    continue;
                }
                if (i == length) {
                    reverseStr(&str, b, i);
                    b = -1;
                    break;
                }
            }
        }
        return str;
    }
    void reverseStr(string* str, int low, int high) {
        if (low == high) return;
        if (str == nullptr) return;
        while (low < high) {
            char temp = (*str)[high];
            (*str)[high] = (*str)[low];
            (*str)[low] = temp;
            low++;
            high--;
        }
    }