Substring with Concatenation of All Words.txt

problem:
You are given a string, S, and a list of words, L, that are all of the same length. Find all starting indices of substring(s) in S that is a concatenation of each word in L exactly once and without any intervening characters.

For example, given:
S: "barfoothefoobarman"
L: ["foo", "bar"]

You should return the indices: [0,9].
(order does not matter).
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solution:
//一拿到这个题，容易一点思路也没有，但由于在L中所有的word长度相同，因此在取字符串上方便很多
//string和map结合使用，substr, find, at
//要考虑到L中可能有重复的单词，所以用map而不是set，有个数量的问题

vector<int> findSubstring(string S, vector<string> &L) 
{
  	map<string, int> word; //放L中所有的字符串，此题的特点是这些字符串等长
	map<string, int> curStr;
	vector<int> ret;
	int N = L.size();
	if(N <= 0)
		return ret;
	for(int i = 0; i < L.size(); i++)
		++word[L.at(i)];
	int M = L.at(0).size();
	int i, j;
	for(i = 0; S.size() >= N * M &&i <= S.size() - N * M; i++)  //这里有个坑，如果S.size() - N * M小于0，得到的实际上是一个很大的数，循环不会停止而一直继续
	{
		curStr.clear();
		for(j = 0; j < N; j++)
		{
			string t = S.substr(i + j * M, M);
			if(word.find(t) == word.end())  //没找到时
				break;
			++curStr[t];
			if(curStr[t] > word[t])  //数量不对时
				break;
		}
		if(j == N)
			ret.push_back(i);		
	}
	return ret;
}