leetcode[186]Reverse Words in a String II

Given an input string, reverse the string word by word. A word is defined as a sequence of non-space characters.

The input string does not contain leading or trailing spaces and the words are always separated by a single space.

For example,
Given s = "

the sky is blue

",
return "

blue is sky the

".

Could you do it in-place without allocating extra space?

class Solution {
public:
//无需额外空间开销
//反转整个字符串, 再反转每个单词
void reverseWords(string &s) {
if(s.length()<1)return;
int i=0,j=s.length()-1;
//去开头结尾的空格
while(s[i]==' '&&i<s.length())
{
i++;
if(i==s.length())
{
s="";
return;
}
}
while(s[j]==' '&&j>=0)
{
j--;
if(j<0)
{
s="";
return;
}
}
if(j-i<0)return;
//截取除去开头结尾空格后的部分，并将其反转
s=s.substr(i,j-i+1);
reverse(s.begin(),s.end());
//对每个以空格隔开的单词再次反转
i=0,j=0;
while(j<s.length())
{
while(s[j]!=' '&&j<s.length())j++;
reverse(s.begin()+i,s.begin()+j);
int tmp=j;
while(s[j]==' '&&j<s.length())j++;
if(tmp+1<s.length())s.erase(s.begin()+tmp+1,s.begin()+j);
//注意此时s的长度已经变短，下边需要减去相应差值
int shortL=j-tmp-1;
j-=shortL;
i=j;
}
return;
}
/**
需额外空间开销
void reverseWords(string &s) {
if(s.empty())return;
string tmp="";
string str="";
int i=0;
while(i<s.length())
{
while(s[i]==' '&&i<s.length())i++;
if(s[i]!=' '&&i<s.length())
{
while(s[i]!=' '&&i<s.length())tmp=s[i++]+tmp;
str+=(tmp+' ');
tmp="";
}
}
reverse(str.begin(),str.end());
int n=str[0]==' '?1:0;
s=str.substr(n,str.size());
return;
}
*/
};