[LeetCode290]Word Pattern

题目：

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.

思路：考察的是字符串模式匹配，可以用map来解决，先将str分割放到一个vector<string>中，再将pattern分割一起放入map<char,string>中，遍历判断是否是对应的键或值即可。

代码：

class Solution {
public:
    bool wordPattern(string pattern, string str) {
        stringstream ss(str);
        string s;
        vector<string> strVec;
        while(ss >> s)
        {   
         strVec.push_back(s);
        }

        if(strVec.size() != pattern.size())
        return false;
        map<char, string> hash;
        int i = 0;
        for(auto c : pattern)
        {
            if(hash.count(c))
            {
                if(hash[c] != strVec[i])
                    return false;
            }
            else
            {
                for(auto p : hash)
                {
                    if(p.second == strVec[i])
                        return false;
                }
                hash[c] = strVec[i];
            }
            ++i;
        }
        return true;
    }
};