## What is the complexity of KNN algorithm?

So for KNN, the time complexity for Training is O(1) which means it is constant and O(n) for testing which means it depends on the number of test examples.

**What is k-nearest neighbors algorithm and explain it with an example?**

KNN works by finding the distances between a query and all the examples in the data, selecting the specified number examples (K) closest to the query, then votes for the most frequent label (in the case of classification) or averages the labels (in the case of regression).

**What is the Nearest Neighbor algorithm?**

What is KNN? K Nearest Neighbour is a simple algorithm that stores all the available cases and classifies the new data or case based on a similarity measure. It is mostly used to classifies a data point based on how its neighbours are classified.

### What is the test time complexity of KNN in KD tree?

Therefore, practical implementations of k-d tree support querying for whole k neighbors at one time and with complexity O(sqrt(n) + k) , which is much better for larger dimensionalities, which are very common in machine learning.

**What is the complexity of K means?**

Abstract: The k-means algorithm is known to have a time complexity of O(n 2 ), where n is the input data size. This quadratic complexity debars the algorithm from being effectively used in large applications.

**Why is the K Nearest Neighbor algorithm lazy?**

Why is the k-nearest neighbors algorithm called “lazy”? Because it does no training at all when you supply the training data. At training time, all it is doing is storing the complete data set but it does not do any calculations at this point.

#### Where KNN algorithm is used?

It’s used in many different areas, such as handwriting detection, image recognition, and video recognition. KNN is most useful when labeled data is too expensive or impossible to obtain, and it can achieve high accuracy in a wide variety of prediction-type problems.

**What is the purpose of K nearest neighbor?**

KNN is a non-parametric, lazy learning algorithm. Its purpose is to use a database in which the data points are separated into several classes to predict the classification of a new sample point.

**What is K nearest neighbor used for?**

K Nearest Neighbor algorithm falls under the Supervised Learning category and is used for classification (most commonly) and regression. It is a versatile algorithm also used for imputing missing values and resampling datasets.

## Is nearest neighbor a greedy algorithm?

The nearest neighbor heuristic is another greedy algorithm, or what some may call naive. It starts at one city and connects with the closest unvisited city. It repeats until every city has been visited. It then returns to the starting city.

**What is time complexity of building kd tree?**

An algorithm that builds a balanced k-d tree to sort points has a worst-case complexity of O(kn log n). This algorithm presorts n points in each of k dimensions using an O(n log n) sort such as Heapsort or Mergesort prior to building the tree.

**What is the difference between k-means and KNN?**

k-Means Clustering is an unsupervised learning algorithm that is used for clustering whereas KNN is a supervised learning algorithm used for classification. KNN is a classification algorithm which falls under the greedy techniques however k-means is a clustering algorithm (unsupervised machine learning technique).

### How do you determine the nearest neighbor of an algorithm?

The number of neighbors is the core deciding factor. K is generally an odd number if the number of classes is 2. When K=1, then the algorithm is known as the nearest neighbor algorithm. This is the simplest case. Suppose P1 is the point, for which label needs to predict.

**What is the normal nearest neighbor problem?**

In the normal nearest neighbor problem, there are a bunch of points (let’s refer to these as training set) in space and given a new point, the objective is to identify the point in the training set closest to the given point.

**What is a Lazy K-nearest neighbor algorithm?**

Given an input vector, KNN calculates the approximate distances between the vectors and then assign the points which are not yet labeled to the class of its K-nearest neighbors. The lazy algorithm means it does not need any training data points for model generation.

#### What is the difference between k-nearest neighbor and k-mean algorithm?

6- The k-mean algorithm is different than K-nearest neighbor algorithm. K-mean is used for clustering and is a unsupervised learning algorithm whereas Knn is supervised leaning algorithm that works on classification problems.