890. Find and Replace Pattern

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1，题目要求
You have a list of words and a pattern, and you want to know which words in words matches the pattern.
A word matches the pattern if there exists a permutation of letters p so that after replacing every letter x in the pattern with p(x), we get the desired word.
(Recall that a permutation of letters is a bijection from letters to letters: every letter maps to another letter, and no two letters map to the same letter.)
Return a list of the words in words that match the given pattern.
You may return the answer in any order.

对单词中的字母按照pattern进行映射，判断是否满足pattern的模式。

2，题目思路
对于这道题，并不是一个简单的模式匹配，而是一个映射的匹配。具体差别就在于，映射的关键在于对应，而不在于具体字母。对于“mee”，我们就可以将其认定为“abb”的方式去映射，也就是“122”的方式。
因此，在具体实现上，就要去寻找这样的map。

3，程序源码

class Solution {
public:
    vector<string> findAndReplacePattern(vector<string>& words, string pattern) {
        string p = normHelper(pattern);
        vector<string> res;
        for(auto w : words) if(normHelper(w) == p)  res.push_back(w);
        return res;
    }
private:
    string normHelper(string s)
    {
        unordered_map<char, int> m;
        for(auto c : s)
            if(m.count(c) == 0)
                m[c] = m.size();
        for(int i = 0;i<s.size();i++)
            s[i] = 'a' + m[s[i]];
        return s;
    }
};