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.

Solution:

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