题解 | #合并表记录#

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

// 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 num = Integer.parseInt(scanner.nextLine());
        Map<Integer, Integer> map = new HashMap<>(num);
        for (int i = 0; i < num; i++) {
            int key = scanner.nextInt();
            int value = scanner.nextInt();
            if (map.get(key) == null) {
                map.put(key, value);
            } else {
                Integer oldValue = map.get(key);
                oldValue += value;
                map.put(key, oldValue);
            }
        }

        List<Integer> sortedList = map.keySet().stream().sorted().collect(
                                       Collectors.toList());
        for (Integer key : sortedList) {
            System.out.println(key + " " + map.get(key));
        }
    }
}