排序数组之间的最长公共子序列

/*
 * LeetCode Problem 1940: Longest Common Subsequence Between Sorted Arrays
 * Problem Description:
 * Given a 2D integer array arrays where each arrays[i] is a sorted array of distinct integers, 
 * return the longest common subsequence between all the arrays.
 * A subsequence is a sequence that can be derived from another sequence by deleting some elements 
 * (possibly none) without changing the order of the remaining elements.
 * 
 * Solution Approach using Java Streams:
 * 1. Use a Map to store the count of each element across all arrays.
 * 2. Use streams to iterate through each array and count the frequency of each element.
 * 3. Filter elements that appear in all arrays and collect them as the result.
 */

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Solution {
    public List<Integer> longestCommonSubsequence(int[][] arrays) {
        Map<Integer, Long> frequencyMap = Stream.of(arrays)
            .flatMapToInt(Arrays::stream)
            .boxed()
            .collect(Collectors.groupingBy(e -> e, Collectors.counting()));
        int numArrays = arrays.length;
        return frequencyMap.entrySet().stream()
            .filter(entry -> entry.getValue() == numArrays)
            .map(Map.Entry::getKey)
            .sorted()
            .collect(Collectors.toList());
    }
}