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Implement sparse vector dot product

Last updated: Mar 29, 2026

Quick Overview

This question evaluates understanding of sparse data representation, memory-efficient data structures, and algorithmic complexity for computing operations like dot products on large but sparsely populated vectors.

  • medium
  • Meta
  • Coding & Algorithms
  • Software Engineer

Implement sparse vector dot product

Company: Meta

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Onsite

You need to implement a data structure for a sparse vector of integers and support efficient computation of the dot product between two such vectors. - The length `n` of the vector can be large (e.g., up to 10^5), but only a small number of positions contain non-zero values. - You are initially given each vector as a dense integer array `nums` of length `n`. Design a `SparseVector` class with: - A constructor `SparseVector(int[] nums)` that stores the vector in a space-efficient way. - A method `int dotProduct(SparseVector other)` that returns the dot product of the current vector with another sparse vector. The dot product of two vectors `a` and `b` of length `n` is defined as: `a · b = a[0]*b[0] + a[1]*b[1] + ... + a[n-1]*b[n-1]`. Specify your data representation, and analyze the time and space complexity of: - Constructing the sparse vector. - Computing the dot product. You do not need to provide actual code, but your algorithm must be clearly described.

Quick Answer: This question evaluates understanding of sparse data representation, memory-efficient data structures, and algorithmic complexity for computing operations like dot products on large but sparsely populated vectors.

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Meta
Dec 8, 2025, 7:54 PM
Software Engineer
Onsite
Coding & Algorithms
2
0

You need to implement a data structure for a sparse vector of integers and support efficient computation of the dot product between two such vectors.

  • The length n of the vector can be large (e.g., up to 10^5), but only a small number of positions contain non-zero values.
  • You are initially given each vector as a dense integer array nums of length n .

Design a SparseVector class with:

  • A constructor SparseVector(int[] nums) that stores the vector in a space-efficient way.
  • A method int dotProduct(SparseVector other) that returns the dot product of the current vector with another sparse vector.

The dot product of two vectors a and b of length n is defined as:

a · b = a[0]*b[0] + a[1]*b[1] + ... + a[n-1]*b[n-1].

Specify your data representation, and analyze the time and space complexity of:

  • Constructing the sparse vector.
  • Computing the dot product.

You do not need to provide actual code, but your algorithm must be clearly described.

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