Intersection of Two Arrays

Problem

Given two integer arrays nums1 and nums2, return an array of their intersection. Each element in the result must be unique and you may return the result in any order.

Examples

The brute-force approach

For every element in nums1, scan all of nums2 to check if it appears there. Collect unique matches.

result = set()
for x in nums1:
    for y in nums2:
        if x == y:
            result.add(x)
return list(result)

O(m×n) — nested loops.

Spotting the pattern

This is a Set problem. The key question to ask yourself:

Why use a set for the result rather than a list? What does using a set give you automatically?

Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.