290. Word Pattern

题目

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.

Example 1:

Input: pattern = "abba", str = "dog cat cat dog"
Output: true

Example 2:

Input:pattern = "abba", str = "dog cat cat fish"
Output: false

Example 3:

Input: pattern = "aaaa", str = "dog cat cat dog"
Output: false

Example 4:

Input: pattern = "abba", str = "dog dog dog dog"
Output: false

Note:

You may assume pattern contains only lowercase letters, and str contains lowercase letters separated by a single space.

题目大意

给定一个模式串，判断字符串是否和给定的模式串，是一样的模式。

解题思路

这道题用 2 个 map 即可。1 个 map 记录模式与字符串的匹配关系，另外一个 map 记录字符串和模式的匹配关系。为什么需要记录双向的关系呢？因为 Example 4 中，a 对应了 dog，这个时候 b 如果再对应 dog 是错误的，所以这里需要从 dog 查询它是否已经和某个模式匹配过了。所以需要双向的关系。

代码

package leetcode

import "strings"

func wordPattern(pattern string, str string) bool {
	strList := strings.Split(str, " ")
	patternByte := []byte(pattern)
	if pattern == "" || len(patternByte) != len(strList) {
		return false
	}

	pMap := map[byte]string{}
	sMap := map[string]byte{}
	for index, b := range patternByte {
		if _, ok := pMap[b]; !ok {
			if _, ok = sMap[strList[index]]; !ok {
				pMap[b] = strList[index]
				sMap[strList[index]] = b
			} else {
				if sMap[strList[index]] != b {
					return false
				}
			}
		} else {
			if pMap[b] != strList[index] {
				return false
			}
		}
	}
	return true
}

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