题解 | #合并表记录#

import java.util.*;

public class Main {
    public static void main(String[] args) {
        HashMap<Integer, Integer> dataset = new HashMap<>();
        Scanner in = new Scanner(System.in);
        int count = in.nextInt();
        int key;
        int value;
        for (int i = 0; i < count; i++) {
            key = in.nextInt();
            value = in.nextInt();
            if (!dataset.containsKey(key)) {
                dataset.put(key, value);
            } else {
                dataset.put(key, value + dataset.get(key));
            }
        }
        in.close();

	  // 用keySet构造TreeSet的时候，就已经可以获取排序（升序）之后的Set
        TreeSet<Integer> keySet = new TreeSet<>(dataset.keySet());

        for (int k : keySet) {
            System.out.println(k + " " + dataset.get(k));
        }
    }
}