找到具有给定和的所有对
给定两个不同元素的大小为n的未排序数组a和大小为m的未排序数组b，任务是从两个数组中查找其和等于x的所有对。
代码：

import java.util.*;
import java.lang.*;
import java.io.*;

class pair  {  
    long first, second;  
    public pair(long first, long second)  
    {  
        this.first = first;  
        this.second = second;  
    }  
}

class GFG {
    public static void main(String[] args) throws IOException
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int t = Integer.parseInt(br.readLine().trim());
        while(t-->0)
        {
            StringTokenizer stt = new StringTokenizer(br.readLine());

            long N = Long.parseLong(stt.nextToken());
            long M = Long.parseLong(stt.nextToken());
            long X = Long.parseLong(stt.nextToken());
            long A[] = new long[(int)(N)];
            long B[] = new long[(int)(M)];

            String inputLine[] = br.readLine().trim().split(" ");
            for (int i = 0; i < N; i++) {
                A[i] = Long.parseLong(inputLine[i]);
            }
            String inputLine1[] = br.readLine().trim().split(" ");
            for (int i = 0; i < M; i++) {
                B[i] = Long.parseLong(inputLine1[i]);
            }

            Solution obj = new Solution();
            pair [] answer = obj.allPairs(A, B, N, M, X);
            int sz = answer.length;

            if(sz==0)
            System.out.println(-1);
            else{
                StringBuilder output = new StringBuilder();
                for(int i=0;i<sz;i++){
                    if(i<sz-1)
                    output.append(answer[i].first +" "+ answer[i].second + ", ");
                    else
                    output.append(answer[i].first +" "+ answer[i].second);

                }
                System.out.println(output);
            }

        }
    }
}
// } Driver Code Ends

//User function Template for Java

/*
class pair  {  
    long first, second;  
    public pair(long first, long second)  
    {  
        this.first = first;  
        this.second = second;  
    }  
}

* /

class Solution {
    public pair[] allPairs( long A[], long B[], long N, long M, long X) {

        //MY CODE STARTS FROM HERE
        ArrayList<Long> list = new ArrayList<>();
        HashSet<Long> set = new HashSet<>();
        for(long i : A){
            set.add(i);
        }

        for(int i=0;i<M;i++){
            if(set.contains(X-B[i])){
                list.add(X-B[i]);
                list.add(B[i]);
            }
        }
        long arr[] = new long[list.size()];
        for(int i=0;i<arr.length;i++){
            arr[i] = list.get(i);
        }
        return arr;
    }
}

我得到这个错误：

prog.java:101: error: incompatible types: long[] cannot be converted to pair[]
        return arr;
               ^
1 error

我如何才能正确地返回答案？