290. Word Pattern

290. 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:
pattern = "abba", str = "dog cat cat dog" should return true.
pattern = "abba", str = "dog cat cat fish" should return false.
pattern = "aaaa", str = "dog cat cat dog" should return false.
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.

Analysis:
这道题跟 205. Isomorphic Strings 思路是一致的。

Source Code（C++）:

#include <iostream>
#include <string>
#include <map>
#include <vector>
using namespace std;

class Solution {
public:
    bool wordPattern(string pattern, string str) {
        vector<int> index_blank;  //记录str中每一个空格的位置。方便起见，标记str首末均为一个空格
        index_blank.push_back(-1);
        for(int i=0; i<str.size(); i++) {
            if (str.at(i) == ' ') {
                index_blank.push_back(i);
            }
        }
        index_blank.push_back(str.size());
        if (pattern.size() != index_blank.size()-1) //判断pattern和str格式长度是否相同
        {
            return false;
        }
        map<string, char> m_str;
        map<char, string> m_pattern;
        for (int i=0; i<pattern.size(); i++)
        {
            string sub_str = str.substr(index_blank[i]+1, index_blank[i+1]-index_blank[i]-1);
            char sub_pattern = pattern.at(i);
            if (m_pattern.find(sub_pattern)!=m_pattern.end() && m_pattern[sub_pattern] != sub_str)
            {
                return false;
            }
            if (m_str.find(sub_str)!=m_str.end() && m_str[sub_str] != sub_pattern)
            {
                return false;
            }
            m_str[sub_str] = sub_pattern;
            m_pattern[sub_pattern] = sub_str;
        }
        return true;
    }
};

int main() {
    Solution sol;
    cout << sol.wordPattern("abba", "dog cat cat dog");
    return 0;
}