翻转字符串

题目：翻转字符串：“student. a am I”。句子应该是“I am a student.”

思路：先把句子整体翻转，然后把每一个单词翻转。

class Solution {
public:
    string ReverseSentence(string str) {
        int length=str.size();
        int i=0,j=0;
        
        if(length==0){
            return str;
        }
        Reverse(str,0,length-1);
        while(i<length){
            if(str[i]==' '){
                Reverse(str,j,i-1);
                j=i+1;
            }
            if(i==length-1){
                Reverse(str,j,i);
                break;
            }
            i++;
        }
        return str;

    }
    void Reverse(string &str,int low,int high){
        while(low<high){
            int tmp=str[low];
            str[low]=str[high];
            str[high]=tmp;
            low++;
            high--;
        }
    }
};