K-Nearest Neighbors (KNN) in ML Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How K affects KNN predictions

In K-Nearest Neighbors, what happens if you increase the value of K too much?

A The model becomes too complex and fits noise, causing overfitting.

B The model ignores all neighbors and predicts randomly.

C The model always predicts the class of the closest neighbor only.

D The model becomes too simple and may miss important patterns, causing underfitting.

❓ Predict Output

intermediate

Output of KNN prediction with given neighbors

Given the following distances and labels of neighbors, what will the KNN predict for K=3?

neighbors = [(0.5, 'A'), (0.7, 'B'), (0.9, 'A'), (1.2, 'B')]

A 'C'

B 'B'

C 'A'

D Error due to invalid neighbors

❓ Hyperparameter

advanced

Choosing the best K value

You have a dataset and want to choose the best K for KNN. Which method is the most reliable to find the best K?

A Use the training data accuracy for each K and pick the highest.

B Use cross-validation to test different K values and pick the one with best average validation accuracy.

C Pick the smallest K to avoid overfitting.

D Pick the largest K to avoid underfitting.

❓ Metrics

advanced

Effect of K on bias and variance

How does increasing K in KNN affect bias and variance?

A Increasing K increases bias and decreases variance.

B Increasing K decreases bias and increases variance.

C Increasing K increases both bias and variance.

D Increasing K decreases both bias and variance.

🔧 Debug

expert

Identifying error in KNN distance calculation

What error does the following code produce when calculating Euclidean distance between two points?

def euclidean_distance(p1, p2):
    return sum((x - y) ** 2 for x, y in zip(p1)) ** 0.5

print(euclidean_distance([1, 2], [4, 6]))

A ValueError: not enough values to unpack (expected 2, got 1)

B TypeError: unsupported operand type(s) for -: 'int' and 'list'

C NameError: name 'y' is not defined

D 0.0 (incorrect distance)