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🧩 Problem Statement

Given two integer arrays nums1 and nums2, return an array of their intersection.

Each element in the result must be unique, and the result can be returned in any order.

🔢 Examples

python

Input: nums1 = [1, 2, 2, 1], nums2 = [2, 2]
Output: [2]

Input: nums1 = [4, 9, 5], nums2 = [9, 4, 9, 8, 4]
Output: [9, 4]  # or [4, 9]

✅ Constraints

• 1 <= nums1.length, nums2.length <= 1000
• 0 <= nums1[i], nums2[i] <= 1000

💡 Key Insight

This is a classic set theory problem:

You need to return the unique elements common to both arrays.

Python’s set data structure makes this problem very easy and efficient.

✅ Solution 1: Using Python Sets (One-liner)

🐍 Python Code

python

class Solution:
    def intersection(self, nums1, nums2):
        return list(set(nums1) & set(nums2))

• set(nums1) and set(nums2) remove duplicates.
• & computes the set intersection.
• Convert back to a list to return the result.

⏱️ Time & Space Complexity

OperationComplexityTimeO(n + m)SpaceO(n + m)

Where n and m are lengths of nums1 and nums2.

✅ Solution 2: Manual Hash Set Check (Step-by-Step)

This approach is helpful for interviews where you want to show the logic clearly.

🐍 Python Code

python

class Solution:
    def intersection(self, nums1, nums2):
        set1 = set(nums1)
        result = set()

        for num in nums2:
            if num in set1:
                result.add(num)
        
        return list(result)

• set1: all unique elements from nums1
• result: store unique intersection elements from nums2

📋 Step-by-Step Walkthrough

Example:

python

nums1 = [1, 2, 2, 1]
nums2 = [2, 2]

• set1 = {1, 2}
• Iterate over nums2:
• 2 → in set1 → add to result
• 2 → already added → skip (sets prevent duplicates)
• Final result = [2]

🧠 Use Cases

• Database queries: find common user IDs
• Text processing: common words in documents
• API: determine shared resource access

✅ Conclusion

LeetCode 349: Intersection of Two Arrays is a great introduction to set operations in Python.

Whether you use built-in operators or write the logic manually, understanding both is useful for coding interviews and real-world applications.

For follow-ups, check out:

• LeetCode 350 – Intersection II (includes duplicates)