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Citadel Interview Guide

Showing 104 questions

Ranking

A question's ranking corresponds to how commonly it's asked by Citadel. The higher the ranking, the more likely you'll encounter it in a Citadel interview.

Question

Frequency

Difficulty

Longest Non-decreasing Subarray From Two Arrays

You're given two arrays. Construct the longest possible non-decreasing subarray by picking elements from either array at each index.

ArraysDynamic Programming

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Medium

#1. Longest Non-decreasing Subarray From Two Arrays

Medium

You're given two arrays. Construct the longest possible non-decreasing subarray by picking elements from either array at each index.

ArraysDynamic Programming

This question is very likely to be asked in your Citadel interview

Minimum Knight Moves

Find the minimum number of moves a knight needs to reach a target position on an infinite chessboard, starting from (0, 0).

Graphs

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Medium

#2. Minimum Knight Moves

Medium

Find the minimum number of moves a knight needs to reach a target position on an infinite chessboard, starting from (0, 0).

Graphs

This question is very likely to be asked in your Citadel interview

Binary Tree Maximum Path Sum

Find the maximum sum of any path in a binary tree, where a path can start and end at any node. The path must contain at least one node.

TreesRecursion

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Hard

#3. Binary Tree Maximum Path Sum

Hard

Find the maximum sum of any path in a binary tree, where a path can start and end at any node. The path must contain at least one node.

TreesRecursion

This question is very likely to be asked in your Citadel interview

Sliding Window Maximum

Find the maximum value within a sliding window of size k as it moves across an array. You'll need to efficiently update the maximum as the window slides.

ArraysSliding Windows

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Hard

#4. Sliding Window Maximum

Hard

Find the maximum value within a sliding window of size k as it moves across an array. You'll need to efficiently update the maximum as the window slides.

ArraysSliding Windows

This question is very likely to be asked in your Citadel interview

Palindromic Substrings

Find the number of palindromic substrings within a given string. Consider each single character and repeated characters as a substring.

StringsDynamic ProgrammingTwo Pointers

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Medium

#5. Palindromic Substrings

Medium

Find the number of palindromic substrings within a given string. Consider each single character and repeated characters as a substring.

StringsDynamic ProgrammingTwo Pointers

This question is very likely to be asked in your Citadel interview

Count Palindromic Subsequences

The problem asks you to find the total number of distinct palindromic subsequences within a given string. Remember that subsequences don't have to be contiguous.

StringsDynamic Programming

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Hard

#6. Count Palindromic Subsequences

Hard

The problem asks you to find the total number of distinct palindromic subsequences within a given string. Remember that subsequences don't have to be contiguous.

StringsDynamic Programming

This question is very likely to be asked in your Citadel interview

Delete and Earn

You're given a list of numbers. By deleting a number, you earn its value, but you must also delete all numbers one less and one greater than it. Maximize the total earned value.

Dynamic ProgrammingArrays

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Medium

#7. Delete and Earn

Medium

You're given a list of numbers. By deleting a number, you earn its value, but you must also delete all numbers one less and one greater than it. Maximize the total earned value.

Dynamic ProgrammingArrays

This question is very likely to be asked in your Citadel interview

Minimum Equal Sum of Two Arrays After Replacing Zeros

You're given two arrays that contain zeros. Replace the zeros in each array with positive integers to maximize the chance of making the two arrays have equal sums. Find the minimum equal sum achievable or determine if it's impossible.

Arrays

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Medium

#8. Minimum Equal Sum of Two Arrays After Replacing Zeros

Medium

Arrays

This question is very likely to be asked in your Citadel interview

Minimum Operations to Make Numbers Non-positive

You're given a list of numbers. Determine the minimum number of operations to make all numbers non-positive by either subtracting or dividing them by a given value.

ArraysGreedy Algorithms

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Hard

#9. Minimum Operations to Make Numbers Non-positive

Hard

You're given a list of numbers. Determine the minimum number of operations to make all numbers non-positive by either subtracting or dividing them by a given value.

ArraysGreedy Algorithms

This question is very likely to be asked in your Citadel interview

LFU Cache

Design and implement a Least Frequently Used (LFU) cache. The cache should allow you to get and put key-value pairs, evicting the least frequently used key when the cache is full.

ArraysLinked ListsDynamic Programming

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Hard

#10. LFU Cache

Hard

Design and implement a Least Frequently Used (LFU) cache. The cache should allow you to get and put key-value pairs, evicting the least frequently used key when the cache is full.

ArraysLinked ListsDynamic Programming

This question is very likely to be asked in your Citadel interview

Maximum Total Damage With Spell Casting

You're given a set of spells with damage and cost. Choose the subset of spells that maximizes your total damage, staying within a given mana limit.

Dynamic ProgrammingArraysGreedy Algorithms

Very likely

If you have a Citadel interview, it's very likely that you will get this question

Medium

#11. Maximum Total Damage With Spell Casting

Medium

You're given a set of spells with damage and cost. Choose the subset of spells that maximizes your total damage, staying within a given mana limit.

Dynamic ProgrammingArraysGreedy Algorithms

This question is very likely to be asked in your Citadel interview

Minimum Costs Using the Train Line

You're given the costs of traveling between cities on a train line, with options to use regular tickets or purchase a travel pass for unlimited rides. Find the minimum total cost to travel to the last city.

Dynamic Programming

Somewhat likely

If you have a Citadel interview, you might get this question

Hard

#12. Minimum Costs Using the Train Line

Hard

Dynamic Programming

This question is somewhat likely to be asked in your Citadel interview

LRU Cache

Design a data structure that acts as a Least Recently Used (LRU) cache. Implement methods to get and put key-value pairs, evicting the least recently used entry when the cache is full.

Linked ListsDynamic Programming

Somewhat likely

If you have a Citadel interview, you might get this question

Medium

#13. LRU Cache

Medium

Design a data structure that acts as a Least Recently Used (LRU) cache. Implement methods to get and put key-value pairs, evicting the least recently used entry when the cache is full.

Linked ListsDynamic Programming

This question is somewhat likely to be asked in your Citadel interview

Best Position for a Service Centre

You're given a set of delivery locations. Find the best spot to build a service center that minimizes the total distance to all locations.

Greedy Algorithms

Somewhat likely

If you have a Citadel interview, you might get this question

Hard

#14. Best Position for a Service Centre

Hard

You're given a set of delivery locations. Find the best spot to build a service center that minimizes the total distance to all locations.

Greedy Algorithms

This question is somewhat likely to be asked in your Citadel interview

Maximum Length of Repeated Subarray

Find the longest common subarray between two given arrays of integers. Return the length of this maximal repeated subarray.

ArraysDynamic Programming

Somewhat likely

If you have a Citadel interview, you might get this question

Medium

#15. Maximum Length of Repeated Subarray

Medium

Find the longest common subarray between two given arrays of integers. Return the length of this maximal repeated subarray.

ArraysDynamic Programming

This question is somewhat likely to be asked in your Citadel interview

First Completely Painted Row or Column

You are given a matrix and a sequence of integers. Determine the index of the first integer in the sequence that results in a fully painted row or column in the matrix.

Arrays

Somewhat likely

If you have a Citadel interview, you might get this question

Medium

#16. First Completely Painted Row or Column

Medium

You are given a matrix and a sequence of integers. Determine the index of the first integer in the sequence that results in a fully painted row or column in the matrix.

Arrays

This question is somewhat likely to be asked in your Citadel interview

Evaluate Division

You are given equations represented by pairs of variables and their corresponding values. Your task is to evaluate queries based on these equations, determining the value of expressions if possible, or returning -1.0 if not.

GraphsStrings

Somewhat likely

If you have a Citadel interview, you might get this question

Medium

#17. Evaluate Division

Medium

GraphsStrings

This question is somewhat likely to be asked in your Citadel interview

Find the Duplicate Number

Given an array of numbers where one number appears more than once, find the duplicate number. You should do this without modifying the original array and using only constant extra space.

Arrays

Somewhat likely

If you have a Citadel interview, you might get this question

Medium

#18. Find the Duplicate Number

Medium

Given an array of numbers where one number appears more than once, find the duplicate number. You should do this without modifying the original array and using only constant extra space.

Arrays

This question is somewhat likely to be asked in your Citadel interview

Serialize and Deserialize Binary Tree

You are given a binary tree. Devise a way to convert the tree into a string representation (serialize) and then reconstruct the tree from that string (deserialize).

TreesRecursion

Somewhat likely

If you have a Citadel interview, you might get this question

Hard

#19. Serialize and Deserialize Binary Tree

Hard

You are given a binary tree. Devise a way to convert the tree into a string representation (serialize) and then reconstruct the tree from that string (deserialize).

TreesRecursion

This question is somewhat likely to be asked in your Citadel interview

Merge Intervals

You are given a collection of intervals. Merge all overlapping intervals into a single interval and return the result.

ArraysGreedy Algorithms

Somewhat likely

If you have a Citadel interview, you might get this question

Medium

#20. Merge Intervals

Medium

You are given a collection of intervals. Merge all overlapping intervals into a single interval and return the result.

ArraysGreedy Algorithms