LeetCode 290. Word Pattern

Description

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

Given a pattern and a string s, find if s 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 s.

Example 1:

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

Example 2:

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

Example 3:

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

Example 4:

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

Constraints:

  • 1 <= pattern.length <= 300
  • pattern contains only lower-case English letters.
  • 1 <= s.length <= 3000
  • s contains only lower-case English letters and spaces ' '.
  • s does not contain any leading or trailing spaces.
  • All the words in s are separated by a single space.

Explanation

Group pattern and string words by their components and record the occurrence positions. Check if the positions are the same.

Python Solution

class Solution:
    def wordPattern(self, pattern: str, s: str) -> bool:
        
        pattern_groups = defaultdict(list)
        for i, c in enumerate(pattern):
            pattern_groups[c].append(i)
            
        word_groups = defaultdict(list)
        words = s.split()
        for i, word in enumerate(words):
            word_groups[word].append(i)
            
        return list(pattern_groups.values()) == list(word_groups.values())
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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