leetcode面试准备: Word Pattern

leetcode面试准备: Word Pattern

1 题目

Given a pattern and a string str, find if str follows the same pattern.

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:

patterncontains only lowercase alphabetical letters, and str contains words separated by a single space. Each word in str contains only lowercase alphabetical letters.

Both pattern and str do not have leading or trailing spaces.

Each letter in pattern must map to a word with length that is at least 1.

接口: public boolean wordPattern(String pattern, String str)

2 思路

题意

通过pattern来匹配单词，很容易想到HashMap思想。

注意

1. pattern的长度，不对应str拆分单词后的长度。
2. 一个pattern字母和唯一一个字符串相互对应。

复杂度: Time:O(n) Space: O(n)

3 代码

public boolean wordPattern(String pattern, String str) {
		String[] words = str.split("\\s", -1);
		int len = words.length;
		if (pattern.length() != len) { // 长度不等直接false，防止后面数组越界
			return false;
		}
		Map<Character, String> map = new HashMap<>(26);
		for (int i = 0; i < len; i++) {
			Character c = pattern.charAt(i);
			if (map.containsKey(c)) {
				if (!map.get(c).equals(words[i]))
					return false;
			} else {
				if (map.containsValue(words[i])) { // 字母和字符串一一对应。
					return false;
				}
				map.put(c, words[i]);
			}
		}
		return true;
	}

4 总结

简单题，注意细节。一次AC。

5 参考

leetcode