LeetCode-in-Java

290. Word Pattern

Easy

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. Specifically:

• Each letter in pattern maps to exactly one unique word in s.
• Each unique word in s maps to exactly one letter in pattern.
• No two letters map to the same word, and no two words map to the same letter.

Example 1:

Input: pattern = “abba”, s = “dog cat cat dog”

Output: true

Explanation:

The bijection can be established as:

• 'a' maps to "dog".
• 'b' maps to "cat".

Example 2:

Input: pattern = “abba”, s = “dog cat cat fish”

Output: false

Example 3:

Input: pattern = “aaaa”, s = “dog cat cat dog”

Output: false

Constraints:

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

Solution

import java.util.HashMap;
import java.util.Map;

public class Solution {
    public boolean wordPattern(String pattern, String s) {
        Map<Character, String> map = new HashMap<>();
        String[] words = s.split(" ");
        if (words.length != pattern.length()) {
            return false;
        }
        for (int i = 0; i < pattern.length(); i++) {
            if (!map.containsKey(pattern.charAt(i))) {
                if (map.containsValue(words[i])) {
                    return false;
                }
                map.put(pattern.charAt(i), words[i]);
            } else {
                if (!words[i].equals(map.get(pattern.charAt(i)))) {
                    return false;
                }
            }
        }
        return true;
    }
}