290. Word Pattern (Easy)

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.

Solution: Hash Table

class Solution {
public:
    bool wordPattern(string pattern, string str) {
        istringstream is(str);
        string chunk; int i = 0;

        unordered_set<string> used;
        unordered_map<char, string> m;
        while (getline(is, chunk, ' ')) {
            if (!m.count(pattern[i])) {
                if (used.count(chunk)) return false;
                used.insert(chunk);
                m[pattern[i]] = chunk;
            } else if (m[pattern[i]] != chunk) return false;
            ++i;
        }
        return i == pattern.size();
    }
};