leetcode Word Pattern

题目连接

https://leetcode.com/problems/word-pattern/  

Word Pattern

Description

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.

class Solution {
public:
	bool wordPattern(string pattern, string str) {
		unordered_map<string, char> A;
		unordered_map<char, string> B;
		size_t p, i, j = 0, n = pattern.length();
		for (i = 0; i < n; i++) {
			char &ch = pattern[i];
			p = str.find(' ', j);
			string ret = str.substr(j, p - j);
			if (A.find(ret) == A.end()) A[ret] = ch;
			else if (A[ret] != ch) return false;
			if (B.find(ch) == B.end()) B[ch] = ret;
			else if (B[ch] != ret) return false;
			j = p + 1;
		}
		return i == pattern.size() && p == string::npos;
	}
};