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Implement Euclidean distance and k-nearest neighbors

PitchbookSoftware Engineer · Onsite

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This question evaluates understanding of Euclidean distance metrics, vector arithmetic, and nearest-neighbor retrieval, testing implementation skills for computing distances and selecting the k closest points.

You are working with points in an n-dimensional Euclidean space, where each point is represented as a list (or array) of numeric coordinates.

Assume:

  • Each point is represented as list[float].
  • For any given operation, all points involved have the same dimensionality (same length of the list).
  • For the k-nearest-neighbors function, assume 1 <= k <= len(dataset).
  • If two points are at exactly the same distance from the query point, break ties by smaller index in the dataset.

1) Compute Euclidean distance between two n-dimensional points

Write a function that computes the Euclidean distance between two points in n-dimensional space.

The function should:

  • Accept two points as input, e.g. p: list[float] and q: list[float].
  • Handle points of arbitrary dimensions (as long as both points have the same dimension).
  • Return the Euclidean distance as a float.

The Euclidean distance between points p and q in n dimensions is:

$$ \text{distance}(p, q) = \sqrt{\sum_{i=1}^{n} (p_i - q_i)^2} $$

Examples:

  • Distance between [1, 2] and [4, 6] in 2D space.
  • Distance between [1, 2, 3] and [4, 5, 6] in 3D space.

You do not need to print anything; just implement the function that returns the distance.


2) Find k-nearest neighbors using Euclidean distance

Using the Euclidean distance function from part (1) as the distance metric, write a function to find the k-nearest neighbors of a query point within a dataset.

The function should:

  • Accept as input:
  • query_vector: list[float] — the query point.
  • k: int — the number of nearest neighbors to return.
  • dataset: list[list[float]] — a list of data points, where each data point is a list of floats of the same dimension as query_vector.
  • Compute the Euclidean distance from the query_vector to each point in dataset.
  • Return a list[int] of the indices of the k nearest neighbors in dataset, sorted in order of increasing distance to the query.
  • If two points have the same distance, return the point with the smaller index first.

Example dataset:

dataset = [
 [10, 11, 12], # index 0
 [1, 2, 3], # index 1
 [4, 5, 6], # index 2
 [7, 8, 9], # index 3
 [13, 14, 15] # index 4
]

Given some query_vector and a value of k, your function should return the indices of the k closest points from this dataset, ordered from closest to farthest.