账户合并

/*
  思路：
  1. 使用Java Stream进行数据处理。
  2. 主要逻辑和上面类似，但使用Stream API来简化代码。
  3. 通过stream进行email到根节点的映射，然后使用stream收集最终结果。
*/
import java.util.*;
import java.util.stream.Collectors;
 
public class SolutionStream {
    private Map<String, String> parent = new HashMap<>();
    private Map<String, String> emailToName = new HashMap<>();
 
    public List<List<String>> accountsMerge(List<List<String>> accounts) {
        accounts.forEach(account -> {
            String name = account.get(0);
            account.stream().skip(1).forEach(email -> {
                parent.putIfAbsent(email, email);
                emailToName.putIfAbsent(email, name);
                union(account.get(1), email);
            });
        });
 
        Map<String, TreeSet<String>> unions = parent.keySet().stream().collect(Collectors.groupingBy(this::find, Collectors.toCollection(TreeSet::new)));
 
        return unions.values().stream()
                .map(emails -> {
                    List<String> account = new ArrayList<>(emails);
                    account.add(0, emailToName.get(account.get(0)));
                    return account;
                })
                .collect(Collectors.toList());
    }
 
    private String find(String email) {
        return parent.get(email).equals(email) ? email : find(parent.get(email));
    }
 
    private void union(String email1, String email2) {
        String root1 = find(email1);
        String root2 = find(email2);
        if (!root1.equals(root2)) {
            parent.put(root1, root2);
        }
    }
}