题解 | #合并表记录#

import java.util.Scanner;
import java.util.*;

// 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 in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别

        int num = in.nextInt();
        Map<Integer, Integer> map = new TreeMap();
        while (num > 0) { // 注意 while 处理多个 case
            int a = in.nextInt();
            int b = in.nextInt();

            if (map.get(a) != null) {
                map.put(a, map.get(a) + b);
            } else {
                map.put(a, b);
            }

            num--;
        }

        Iterator it = map.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<Integer, Integer> entry = (Map.Entry<Integer, Integer>) it.next();
            System.out.println(entry.getKey() + " " + entry.getValue());
        }
    }
}