leetcode 290. Word Pattern

Given a pattern and a string str, find if str follows the same pattern.

Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in str.

Examples:

1. pattern = "abba", str = "dog cat cat dog" should return true.
2. pattern = "abba", str = "dog cat cat fish" should return false.
3. pattern = "aaaa", str = "dog cat cat dog" should return false.
4. pattern = "abba", str = "dog dog dog dog" should return false.

Notes:
You may assume pattern contains only lowercase letters, and str contains lowercase letters separated by a single space.

class Solution {
public:
	bool wordPattern(string pattern, string str) {

		map<char, string>trans;
		set<string>hist;
		for (int i = 0; i < pattern.size() - 1; i++)
		{
			int pos = str.find(' ');
			if (pos == string::npos)
				return false;
			string s = string(str.begin(), str.begin() + pos);
			if (trans.find(pattern[i]) == trans.end())
			{
				if (hist.find(s) != hist.end())
					return false;
				hist.insert(s);
				trans[pattern[i]] = s;
			}
			else
			{
				if (trans[pattern[i]] != s)
					return false;
			}
			str.erase(0, pos + 1);
		}
		if (trans.find(pattern.back()) == trans.end())
		{
			if (hist.find(str) != hist.end())
				return false;
		}
		else
		{
			if (trans[pattern.back()] != str)
				return false;
		}
		return true;
	}
};

accept