Find all pairs with a given sum

Easy

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.

Note: All pairs should be printed in increasing order of u. For eg. for two pairs (u₁,v₁) and (u₂,v₂), if u₁ < u₂ then
(u₁,v₁) should be printed first else second.

Example 1:

Input:
A[] = {1, 2, 4, 5, 7}
B[] = {5, 6, 3, 4, 8} 
X = 9 
Output: 
1 8
4 5 
5 4
Explanation:
(1, 8), (4, 5), (5, 4) are the
pairs which sum to 9.

Example 2:

Input:
A[] = {-1, -2, 4, -6, 5, 7}
B[] = {6, 3, 4, 0} 
X = 8 
Output:
4 4 
5 3

Your Task:  
You don't need to read input or print anything. Your task is to complete the function allPairs() which takes the array A[], B[], its size N and M respectively, and an integer X as inputs and returns the sorted vector pair values of all the pairs u,v where u belongs to array A and v belongs to array B. If no such pair exists return empty vector pair.

Expected Time Complexity: O(NLog(N))
Expected Auxiliary Space: O(N)

Constraints:
1 ≤ N, M ≤ 10⁶
-10⁶ ≤ X, A[i], B[i] ≤ 10⁶