题解 | #合并表记录#

import java.util.Scanner;
import java.util.Map;
import java.util.HashMap;
import java.util.Set;
import java.util.Collections;
import java.util.TreeSet;
import java.util.Comparator;
// 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);
        int n = in.nextInt();
        Map<Integer, Integer> map = new HashMap<>();
        for(int i = 0; i < n; i++){
            int index = in.nextInt();
            int value = in.nextInt();
            if(map.get(index) == null){
                map.put(index, value);
            }else{
                map.put(index, map.get(index) + value);
            }
        }
        Set<Integer> keys = map.keySet();
        TreeSet<Integer> treeSet = new TreeSet<>(new Comparator<Integer>(){
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1.compareTo(o2);
            }
        });
        treeSet.addAll(keys);
        for(int key: treeSet){
            System.out.println(key + " " + map.get(key));
        }
    }
}