Citadel Interview Questions

Implement the native map function for arrays.

In C++, would you prefer to store pointers or references in a vector? Explain your reasoning.

In C++ templates, in what cases is the keyword 'typename' used?

How do you implement a hash map in C#?

What is the expected value when rolling two fair six-sided dice?

Write code to compute x raised to the power n (x^n) in O(log n) time.

Implement the k-nearest neighbor algorithm.

Given a vector of edges (e.g., A-B, A-C, C-D), write a function to determine if the resulting graph is a tree. If it is a tree, return its root.

Implement a class for the game Connect Four.

Find the number of pairs of indices (i, j) in an array v such that v[i] = v[j] = v[i+1] + v[i+2] + ... + v[j-1]. Design an algorithm with time complexity O(n log n).

If a Binary Search Tree was implemented incorrectly, such that a number to the left of a node is not smaller as it should be, how would you detect this mistake? What is the most efficient way to identify such an error?

Two people plan to meet at a train station. Each arrives at a random time between 4:00 pm and 5:00 pm and will wait 10 minutes for the other. What is the probability that they will meet?

What is implied volatility? What is the probability distribution of X + Y, where X and Y are independent and identically distributed uniform random variables?

Given a list of stock prices for consecutive days, determine the optimal strategy to maximize profit from buying and selling stocks. You may complete as many transactions as you like (i.e., buy and sell multiple times), but you must sell the stock before you buy again.

1. Given a triangle defined by its vertices, determine whether a given point is inside the triangle. 2. Given a list of times, find the number of pairs of times that add up to 60.

Explain why the volatility smile exists.

You are tossing a fair coin. What is the expected number of tosses until you get two heads in a row?

If 0.1% of people have a certain disease, and you have a test that is correct 99% of the time, what is the probability that someone who tests positive actually has the disease?

What is the expected value of the sum when rolling two fair six-sided dice?

Given a biased coin (with probability p of landing heads), what is the probability of flipping two heads (HH) in two consecutive tosses?

Describe how the random forest algorithm works.