0290. Word Pattern (E)

Word Pattern (E)

题目

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.

Example 1:

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

Example 2:

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

Example 3:

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

Example 4:

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

Notes:
You may assume pattern contains only lowercase letters, and str contains lowercase letters that may be separated by a single space.

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题意

判断pattern中的字符是不是和str中的非空单词字符子串一一对应。

思路

用HashMap实现，注意必须要一对一，不存在多对一的情况。

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代码实现

Java

class Solution {
    public boolean wordPattern(String pattern, String str) {
        Map<Character, String> hash = new HashMap<>();
        String[] s = str.split(" ");
        int i = 0;

        if (pattern.length() != s.length) {
            return false;
        }

        for (char c : pattern.toCharArray()) {
            if (!hash.containsKey(c)) {
              	// 必须一一对应，不能多对一
                if (hash.containsValue(s[i])) {
                    return false;
                }
                hash.put(c, s[i++]);
            } else if (!hash.get(c).equals(s[i])) {
                return false;
            } else {
                i++;
            }
        }

        return true;
    }
}