单词子集

/*
 * 思路：
 * 1. 通过流计算 words2 中每个字母的最大频率。
 * 2. 使用流过滤和收集 words1 中满足条件的单词。
 */

import java.util.*;
import java.util.function.Function;
import java.util.stream.Collectors;

public class SolutionStream {
    public List<String> wordSubsets(String[] words1, String[] words2) {
        int[] maxFreq = Arrays.stream(words2)
                .map(this::countFreq)
                .reduce(new int[26], (acc, bFreq) -> {
                    for (int i = 0; i < 26; i++) {
                        acc[i] = Math.max(acc[i], bFreq[i]);
                    }
                    return acc;
                });

        return Arrays.stream(words1)
                .filter(a -> isUniversal(countFreq(a), maxFreq))
                .collect(Collectors.toList());
    }

    private int[] countFreq(String s) {
        return s.chars().map(c -> c - 'a').collect(() -> new int[26], (arr, c) -> arr[c]++, (arr1, arr2) -> {
            for (int i = 0; i < 26; i++) {
                arr1[i] += arr2[i];
            }
        });
    }

    private boolean isUniversal(int[] aFreq, int[] maxFreq) {
        return IntStream.range(0, 26).allMatch(i -> aFreq[i] >= maxFreq[i]);
    }
}