【leetcode】word-break-ii

题目：

Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word.

Return all such possible sentences.

For example, given

s ="catsanddog",

dict =["cat", "cats", "and", "sand", "dog"].

A solution is["cats and dog", "cat sand dog"].

代码分析：

void _wordBreak(vector<string> &ret,
						string str,//表示的是要操作的字符串
						string &src,//表示的题目给的字符串
						int idex,///当前的字符串走到哪个位置
						unordered_set<string> &dict,
						set<int>& size
						)
{
	//表示已经走完了
	if(idex == src.size())
	{
		if(str.size() != 0)
			ret.push_back(str);
		return  ;
	}
	//要是当前的字符串为不为空的话，那么在尾部加上空格 
	if(idex != 0)
		str.push_back(' ');
	set<int>::iterator len = size.begin();
	for(; len!= size.end();++len)
	{
		int i= *len;
		if(idex + i > src.size()||i==0)
			break;
		string  tmp((char*)src.c_str()+idex,(char*)src.c_str()+idex+i);	
		unordered_set<string>::iterator it  = dict.find(tmp);
        if(it != dict.end())
			_wordBreak(ret,str+tmp,src,idex+i,dict,size);
	}
}
vector<string> wordBreak(string s, unordered_set<string> &dict) {
	vector<string> ret;
	if(s.size() == 0||dict.empty() == true)
		return ret;
	unordered_set<string>::iterator it  = dict.begin();
	set<int> size;
	while(it!= dict.end())
	{
		size.insert(it->size());
		++it;
	}
	string  str;
	_wordBreak(ret,str,s,0,dict,size);
	return ret;
}