Word Pattern

描述

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.

分析

本题跟 "Isomorphic Strings" 很类似，用两个HashMap, 记录从字符到字符串和字符串到字符的映射。

代码

  1. // Word Pattern
  2. // Time Complexity: O(n), Space Complexity: O(n)
  3. public class Solution {
  4.     public boolean wordPattern(String pattern, String str) {
  5.         String[] words = str.split(" ");
  6.         if (words.length != pattern.length()) return false;
  8.         final Map<Character, String> map1 = new HashMap<>();
  9.         final Map<String, Character> map2 = new HashMap<>();
  10.         for (int i = 0; i < words.length; ++i) {
  11.             final Character key1 = pattern.charAt(i);
  12.             if (map1.containsKey(key1)) {
  13.                 final String value = map1.get(key1);
  14.                 if (!value.equals(words[i])) return false;
  15.             } else {
  16.                 map1.put(key1, words[i]);
  17.             }
  19.             final String key2 = words[i];
  20.             if (map2.containsKey(key2)) {
  21.                 final char value = map2.get(key2);
  22.                 if (value != pattern.charAt(i)) return false;
  23.             } else {
  24.                 map2.put(key2, pattern.charAt(i));
  25.             }
  26.         }
  27.         return true;
  28.     }
  29. }

相关题目

原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/java/string/word-pattern.html