[LeetCode]48. Word Pattern匹配模式

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.

解法1：遍历pattern，保存好当前的模式，同时遍历str，也保存下str的模式，二者匹配。

class Solution {
public:
    bool wordPattern(string pattern, string str) {
        int ps = pattern.size(), ss = str.size();
        vector< pair<char, int> > vc;
        vector< pair<string, int> > vs;
        int i = 0, j = 0, k = 0;
        for(; i < ps; ++i)
        {
            vector< pair<char, int> >::iterator iter1 = keyFind(vc.begin(), vc.end(), pattern[i]);
            if(iter1 == vc.end()) vc.push_back(make_pair(pattern[i], 1));
            else iter1->second += 1;

            while(j < ss && str[j] == ' ') ++j;
            k = j;
            while(j < ss && str[j] != ' ') ++j;
            if(k == j) return false;
            string s(str.begin() + k, str.begin() + j);
            vector< pair<string, int> >::iterator iter2 = keyFind(vs.begin(), vs.end(), s);
            if(iter2 == vs.end()) vs.push_back(make_pair(s, 1));
            else iter2->second += 1;

            if(!sameVec(vc, vs)) return false;
        }
        return j == ss ? true : false;
    }
private:
    bool sameVec(const vector< pair<char, int> >& vc, const vector< pair<string, int> >& vs)
    {
        int vcs = vc.size(), vss = vs.size();
        if(vcs != vss) return false;
        for(int i = 0; i < vcs; ++i)
            if(vc[i].second != vs[i].second) return false;
        return true;
    }
    template<typename T>
    const typename vector< pair<T, int> >::iterator keyFind(const typename vector< pair<T, int> >::iterator beg, const typename vector< pair<T, int> >::iterator end, const T& patt)
    {
        typename vector< pair<T, int> >::iterator iter = beg;
        while(iter != end && iter->first != patt) ++iter;
        return iter;
    }
};

解法2：使用Hash Map。实际上这题是一个一一映射的问题。

class Solution {
public:
    bool wordPattern(string pattern, string str) {
        int ps = pattern.size(), ss = str.size();
        int i = 0, j = 0, k = 0, cnt = 0;
        vector<string> cts(256, ""); //pattern中的字符映射到str中的单词
        map<string, char> stc; //str中的单词映射到pattern中的字符
        vector<int> flag(256, 0); //pattern中的字符是否已有了在str中的映射
        for (; i < ps; ++i)
        {
            while (j < ss && str[j] == ' ') ++j;
            k = j;
            while (j < ss && str[j] != ' ') ++j;
            string word(str.begin() + k, str.begin() + j);
            ++cnt;
            if (flag[pattern[i]] == 0)
            {
                if (stc.find(word) == stc.end())
                {
                    cts[pattern[i]] = word;
                    flag[pattern[i]] = 1;
                    stc[word] = pattern[i];
                }
                else return false; //str中相同的单词映射到了pattern中不同的字符
            }
            else if (word != cts[pattern[i]]) return false; //pattern中的相同的字符映射到了str中两个不同的单词
            if (j == ss) break;
        }
        if (cnt != ps || j != ss) return false; //str中单词数目和pattern中字符数目不一致
        else return true;
    }
};