LeetCode 290. Word Pattern

word-pattern.java

/**
 * https://leetcode.com/problems/word-pattern/
 *
 * O(n) runtime, O(n) space
 *
 * simply verify it is a bijection by using HashSet and HashMap
 * use HashMap to verify that if a = b, then f(a) = f(b)
 * use HashSet to verify that if f(a) = f(b), then a = b
 */

public class Solution {
    public boolean wordPattern(String pattern, String str) {
        String[] strs = str.split(" "); // note str.split(" ") here
        if (pattern.length() != strs.length) {
            return false;
        }
        HashSet<String> set = new HashSet<>();
        HashMap<Character, String> map = new HashMap<>();
        for (int i = 0; i < pattern.length(); i++) {
            char key = pattern.charAt(i);
            String value = strs[i];
            if (map.containsKey(key)) {
                if (!map.get(key).equals(value)) {
                    return false;
                }
            } else if (set.contains(value)) {
                return false;
            } else {
                set.add(value);
                map.put(key, value);
            }
        }
        return true;
    }
}