Question
You are given two integer lists a and b and a target integer. Count how many ordered index pairs (i, j) satisfy a[i] + b[j] == target, where i indexes into a and j indexes into b. Every index pair counts separately, even when values repeat. For example, with a = [1, 2, 2], b = [3, 2] and target 4, the pairs are (0,0), (1,1) and (2,1), so the answer is 3. Comparing every element of a with every element of b is too slow for large inputs — do better using a hash map.
cross_pair_count(a: list[int], b: list[int], target: int) → int[[1,2,2],[3,2],4]out3State your approach and its time/space complexity out loud before you optimize. Handle the edge cases (empty input, duplicates, overflow), and say why you chose this over the brute force. Green tests are the floor, not the grade.
Vibe coding: describe the solution in plain language (or narrate it) and the coach grades your approach. Generating runnable code from your description is coming next.