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Sort an array with user defined datatype in java

This question is from geeksforgeeks :

Here’s the link: https://practice.geeksforgeeks.org/problems/find-all-pairs-whose-sum-is-x5808/1#

Q) Given two unsorted arrays A of size N and B of size M of distinct elements, the task is to find all pairs from both arrays whose sum is equal to X.

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<pair> 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(new pair(X-B[i], B[i]));
            }
        }
        
        pair arr[] = new pair[list.size()];
        arr = list.toArray(arr);
        for(int j=0;j<(arr.length-1);j++){
            if(arr[j]>arr[j+1]){
                pair temp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = temp;
                j -= 1;
            }
            
        }
        return arr;
    }
}

I have to sort the result in ascending order but the datatype for array here is user-defined (i.e. pair). So I am getting this error :

prog.java:100: error: bad operand types for binary operator ‘>’ if(arr[j]>arr[j+1]){ ^ first type: pair second type: pair 1 error

Please help me sort the array. Note: Time complexity should be O(nlogn)

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Answer

Why use the custom sort when you can use built-in sort in Java list.

Just use list.sort(Comparator.comparing(p -> ((pair) p).first).thenComparing(p -> ((pair) p).second)); to sort the pair list.

public pair[] allPairs( long A[], long B[], long N, long M, long X) {
        // Your code goes here
        //MY CODE STARTS FROM HERE
        ArrayList<pair> 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(new pair(X-B[i], B[i]));
            }
        }

        list.sort(
                Comparator
                        .comparing(p -> ((pair) p).first)
                        .thenComparing(p -> ((pair) p).second)
        );
        return list.toArray(pair[]::new);
    }
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