直接把系数加1000映射到数组下标就行

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[] nums1 = new int[2000];
        int[] nums2 = new int[2000];
        int m = sc.nextInt();
        while (m-- > 0) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            nums1[b + 1000] = a;
        }
        int n = sc.nextInt();
        while (n-- > 0) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            nums2[b + 1000] = a;
        }
        for (int i = 1999; i >= 0; i--) {
            int num = nums1[i] + nums2[i];
            if (num != 0) System.out.print(num + " " + (i - 1000) + " ");
        }
    }
}