题解 | #合并表记录#

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args)  {
        Scanner scanner = new Scanner(System.in);
        int tableSize = scanner.nextInt();
        Map<Integer, Integer> table = new HashMap<>(tableSize);
        for (int i = 0; i < tableSize; i++) {
            int key = scanner.nextInt();
            int value = scanner.nextInt();
            if (table.containsKey(key)) {
                table.put(key, table.get(key) + value);
            } else {
                table.put(key, value);
            }
        }
        Set<Map.Entry<Integer, Integer>> entries = table.entrySet();

        List<Map.Entry<Integer, Integer>> entries1 = new ArrayList<>(entries);

        Collections.sort(entries1, new Comparator<Map.Entry<Integer, Integer>>() {
            @Override
            public int compare(Map.Entry<Integer, Integer> o1,
                               Map.Entry<Integer, Integer> o2) {
                return o1.getKey() - o2.getKey();
            }
        });
        for (Map.Entry<Integer, Integer> entry : entries1) {
            System.out.println(entry.getKey() + " " + entry.getValue());
        }
    }
}