Is Intersection of Multiple Arrays easy or hard?

Intersection of Multiple Arrays is classified as an Easy problem on LeetCode. The main idea is recognizing that either frequency counting or set intersection can efficiently track elements that appear in every array.

Intersection of Multiple Arrays Python/Java solution

Python solutions commonly use dictionaries or the built-in set intersection operator. Java implementations typically use HashMap for counting or HashSet with retainAll operations. Both approaches run in linear time relative to the total input size.

How to solve Intersection of Multiple Arrays in O(n)?

Use a hash map to count occurrences across arrays. Iterate through every number and increment its count. After processing all arrays, collect numbers whose count equals the number of arrays. This makes the main computation O(N) with an additional sorting step for the final output.

What is the best approach for Intersection of Multiple Arrays?

The most common approach uses a hash map to count how many arrays contain each number. After scanning all arrays, numbers with frequency equal to the total number of arrays belong to the intersection. This runs in O(N) time for counting plus sorting of the result.

Is Intersection of Multiple Arrays asked at Google/Amazon/Meta?

Problems involving array intersection and hash map counting frequently appear in interviews at companies like Amazon, Google, and Meta. Variations include intersecting two arrays, finding common elements across multiple lists, or computing frequency-based intersections.

What data structure is used in Intersection of Multiple Arrays?

The primary data structures are hash maps for counting frequencies and hash sets for intersection operations. These structures provide average O(1) lookup and insertion, which keeps the algorithm efficient even with many elements.

What is the time complexity of Intersection of Multiple Arrays?

The counting or set-based solution processes each element once, giving O(N) time where N is the total number of elements across all arrays. The final result must be sorted, which adds O(K log K) where K is the size of the intersection.

Description Hints 2 Solution Video 6:10

2248. Intersection of Multiple Arrays

Easy68.8% acceptance2 companies

Given a 2D integer array nums where nums[i] is a non-empty array of distinct positive integers, return the list of integers that are present in each array of nums sorted in ascending order.

Example 1:

Input: nums = [[3,1,2,4,5],[1,2,3,4],[3,4,5,6]]
Output: [3,4]
Explanation: 
The only integers present in each of nums[0] = [3,1,2,4,5], nums[1] = [1,2,3,4], and nums[2] = [3,4,5,6] are 3 and 4, so we return [3,4].

Example 2:

Input: nums = [[1,2,3],[4,5,6]]
Output: []
Explanation: 
There does not exist any integer present both in nums[0] and nums[1], so we return an empty list [].

Constraints:

1 <= nums.length <= 1000
1 <= sum(nums[i].length) <= 1000
1 <= nums[i][j] <= 1000
All the values of nums[i] are unique.

Asked at 2 companies

Uber Meta

Topics

Hints open one at a time

Hint 1

Keep a count of the number of times each integer occurs in nums.

Hint 2

Since all integers of nums[i] are distinct, if an integer is present in each array, its count will be equal to the total number of arrays.

6:10

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