🧩 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 <= 10000 <= 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 nums1result: 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)