题解 | #合并表记录#

import java.util.*;
import java.util.stream.*;
import java.io.*;

public class Main{
    public static void main(String[]args){
        Map<Integer,Integer> m = new HashMap<>();
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int a =0 ,b = 0;
        for(int i=0;i<n;i++){
            //一边输入一边计算，hashMap
            a=sc.nextInt();
            b=sc.nextInt();
            if(m.containsKey(a)){
                m.put(a,m.get(a) + b);
            }else{
                m.put(a,b);
            }
        }
        List<Integer> sortedList = m.keySet().stream().sorted(Comparator.naturalOrder()).collect(Collectors.toList());
        for (Integer k : sortedList) {
            System.out.println(k + " " + m.get(k));
        }
    }
}