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？

class Solution {
public:
    string ReverseSentence(string str) {

        int len = str.size();

        if (len <=1){
            return str;
        }

        int left = 0, right = len - 1;

        reverseStr(str, left, right);

        left = 0;
        right = 0;
        while(right <= len){

            //“wonderful”这种情况，也就是处理最后一个词
            if (right==len || str[right] == ' ' ){
                reverseStr(str, left, right - 1);
                right++;
                left = right;
            }
            else{
                right++;
            }
        }
        return str;
    }
private:
    void reverseStr(string &str,int left,int right){
        while (left < right){
            swap(str[left], str[right]);
            left++;
            right--;
        }
    }

};

书上代码
可以发现C++中string是可以访问到size()这个位置的，而且值为’\0’

class Solution {
public:
    string ReverseSentence(string str) {

        int len = str.size();

        if (len <=1){
            return str;
        }

        int left = 0, right = len - 1;

        reverseStr(str, left, right);

        left = 0;
        right = 0;
        while(str[left]!= '\0'){

            if (str[left] == ' '){
                left++;
                right++;
            }
            else if (str[right] == ' ' || str[right] == '\0'){
                reverseStr(str, left, --right);
                right++;
                left = right;
            }
            else{
                right++;
            }
        }

        return str;
    }
private:
    void reverseStr(string &str,int left,int right){
        while (left < right){
            swap(str[left], str[right]);
            left++;
            right--;
        }
    }

};