[LeetCode] 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.

给定一个模式串pattern和一个字符串str，找到如果str是否遵循相同的模式。

使用了map、set、vector三种容器。利用map来存储模式串字符与字符串中字符串的对应关系，利用set的性质来检测pattern与str中的对应元素是否一一对应，利用vector存储str中去除空格后的每一个单词。

最后用map中模板的值构建新的字符串观察是否与给定的str相等。

总的来说是一个分离+重构+比较的过程。

class Solution {
public:
    bool wordPattern(string pattern, string str) {
        istringstream istr(str);
        string s;
        vector<string> svec;
        while (istr >> s)
            svec.push_back(s);
        if (pattern.size() != svec.size())
            return false;
        unordered_map<char, string> c2s;
        unordered_set<char> cs;
        unordered_set<string> ss(svec.begin(), svec.end());
        for (char c : pattern)
            cs.insert(c);
        if (cs.size() != ss.size())
            return false;
        for (int i = 0; i != pattern.size(); i++) {
            c2s[pattern[i]] = svec[i];
        }
        string tmp;
        for (auto c : pattern) {
            tmp += (c2s[c] + " ");
        }
        if (tmp != str + " ")
            return false;
        return true;
    }
};
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