用户网站访问行为分析

// Leetcode Problem 1152: Analyze User Website Visit Pattern using Java Streams
// The task is to find the most visited pattern of length 3 (3 websites) by any user.
// If there are multiple patterns with the same highest frequency, return the lexicographically smallest one.

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

public class Solution {
    public List<String> mostVisitedPattern(String[] username, int[] timestamp, String[] website) {
        // Step 1: Combine the inputs into a list of Visit objects
        List<Visit> visits = IntStream.range(0, username.length)
                                      .mapToObj(i -> new Visit(username[i], timestamp[i], website[i]))
                                      .sorted(Comparator.comparingInt(v -> v.timestamp))
                                      .collect(Collectors.toList());

        // Step 2: Create a map from user to their list of websites
        Map<String, List<String>> userWebsites = visits.stream()
                                                       .collect(Collectors.groupingBy(v -> v.username, Collectors.mapping(v -> v.website, Collectors.toList())));

        // Step 3: Count all 3-sequence patterns for each user
        Map<List<String>, Integer> patternCount = new HashMap<>();
        userWebsites.values().forEach(websites -> {
            if (websites.size() < 3) return;
            Set<List<String>> seen = new HashSet<>();
            for (int i = 0; i < websites.size() - 2; i++) {
                for (int j = i + 1; j < websites.size() - 1; j++) {
                    for (int k = j + 1; k < websites.size(); k++) {
                        List<String> pattern = Arrays.asList(websites.get(i), websites.get(j), websites.get(k));
                        if (seen.add(pattern)) {
                            patternCount.put(pattern, patternCount.getOrDefault(pattern, 0) + 1);
                        }
                    }
                }
            }
        });

        // Step 4: Find the most frequent pattern
        return patternCount.entrySet().stream()
                           .max(Map.Entry.<List<String>, Integer>comparingByValue()
                           .thenComparing(Map.Entry::getKey, (a, b) -> a.toString().compareTo(b.toString())))
                           .map(Map.Entry::getKey)
                           .orElse(Collections.emptyList());
    }

    class Visit {
        String username;
        int timestamp;
        String website;

        Visit(String u, int t, String w) {
            username = u;
            timestamp = t;
            website = w;
        }
    }
}