Word Pattern问题及解法

问题描述：

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.

示例：

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.

问题分析：

利用hashtable，将pattern中的每个字符映射成int，str的每个单词同样也映射成int，两者对比，若有映射不相同的，即视为不匹配。

过程详见代码：

class Solution {public:    bool wordPattern(string pattern, string str) {        map<char,int> p2i;        map<string,int> w2i;        istringstream in(str);        int i = 0, n = pattern.size();        for(string word; in >> word; i++)        {        if(i == n || p2i[pattern[i]] != w2i[word]) return false;        p2i[pattern[i]] = w2i[word] = i + 1;}return i == n;    }};