Leetcode 2761. Prime Pairs With Target Sum

Find all prime pairs (x, y) with 1 ≤ x ≤ y ≤ n and x + y = n, returning them sorted by x. With n ≤ 10^6 this is typically done by precomputing primes up to n (e.g., sieve) and checking complements for x in [2, n/2].