Problem database last updated: June 20, 2025
25 problems · 5 Easy, 17 Medium, 3 Hard · Ranked #78 of 458
5 Easy
20% · avg 23%
17 Medium
68% · avg 59%
3 Hard
12% · avg 18%
Based on 25 reported problems, Palo Alto Networks interviews are in line with industry averages - 12% Hard vs 18% overall. The majority (68%) of questions are Medium difficulty, which is typical for companies that want to see solid fundamentals without excessive trick questions.
Compared to the industry average, Palo Alto Networks puts unusual emphasis on trie (8% of problems, 3x the industry average), design (16% of problems, 2.8x the industry average), sliding-window (12% of problems, 2.6x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are array (56%), string (44%), hash-table (36%), design (16%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
LRU Cache Design a data structure that follows the constraints of a Least Recently Used (LRU) cache. | Medium | Very Likely | hash-tablelinked-listdesign | Solve |
Find the Longest Equal Subarray You are given a 0-indexed integer array nums and an integer k. | Medium | Very Likely | arrayhash-tablebinary-search | Solve |
Longest Substring Without Repeating Characters Given a string s, find the length of the longest substring without duplicate characters. | Medium | Very Likely | hash-tablestringsliding-window | Solve |
Median of Two Sorted Arrays Given two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays. | Hard | Very Likely | arraybinary-searchdivide-and-conquer | Solve |
String Compression Given an array of characters chars, compress it using the following algorithm: | Medium | Very Likely | two-pointersstring | Solve |
Maximum Length of a Concatenated String with Unique Characters You are given an array of strings arr. A string s is formed by the concatenation of a subsequence of arr that has unique characters. | Medium | Likely | arraystringbacktracking | Solve |
Group Anagrams Given an array of strings strs, group the anagrams together. You can return the answer in any order. | Medium | Likely | arrayhash-tablestring | Solve |
Binary Tree Level Order Traversal Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level). | Medium | Likely | treebreadth-first-searchbinary-tree | Solve |
Insert Delete GetRandom O(1) Implement the RandomizedSet class: | Medium | Likely | arrayhash-tablemath | Solve |
Minimum Path Sum Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right, which minimizes the sum of all numbers along its path. | Medium | Likely | arraydynamic-programmingmatrix | Solve |
Sliding Window Maximum You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see... | Hard | Likely | arrayqueuesliding-window | Solve |
Min Stack Design a stack that supports push, pop, top, and retrieving the minimum element in constant time. | Medium | Likely | stackdesign | Solve |
Two Sum Given an array of integers nums and an integer target, return the indices of the two numbers that add up to target. | Easy | Likely | arrayhash-map | Solve |
Valid Parentheses Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. | Easy | Likely | stringstack | Solve |
Shortest Path in Binary Matrix Given an n x n binary matrix grid, return the length of the shortest clear path in the matrix. If there is no clear path, return -1. | Medium | Likely | arraybreadth-first-searchmatrix | Solve |
Word Break Given a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words. | Medium | Likely | arrayhash-tablestring | Solve |
Basic Calculator Given a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation. | Hard | Likely | mathstringstack | Solve |
Merge Sorted Array You are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and num... | Easy | Likely | arraytwo-pointerssorting | Solve |
Design HashMap Design a HashMap without using any built-in hash table libraries. | Easy | Likely | arrayhash-tablelinked-list | Solve |
Integer to Roman Seven different symbols represent Roman numerals with the following values: | Medium | Likely | hash-tablemathstring | Solve |
Search in Rotated Sorted Array There is an integer array nums sorted in ascending order (with distinct values). | Medium | Likely | arraybinary-search | Solve |
Merge Two Sorted Lists You are given the heads of two sorted linked lists list1 and list2. | Easy | Likely | linked-listrecursion | Solve |
Restore IP Addresses A valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros. | Medium | Likely | stringbacktracking | Solve |
Top K Frequent Words Given an array of strings words and an integer k, return the k most frequent strings. | Medium | Likely | arrayhash-tablestring | Solve |
Longest Palindromic Substring Given a string s, return the longest palindromic substring in s. | Medium | Likely | two-pointersstringdynamic-programming | Solve |
LRU Cache
SolveDesign a data structure that follows the constraints of a Least Recently Used (LRU) cache.
Find the Longest Equal Subarray
SolveYou are given a 0-indexed integer array nums and an integer k.
Longest Substring Without Repeating Characters
SolveGiven a string s, find the length of the longest substring without duplicate characters.
Median of Two Sorted Arrays
SolveGiven two sorted arrays nums1 and nums2 of size m and n respectively, return the median of the two sorted arrays.
String Compression
SolveGiven an array of characters chars, compress it using the following algorithm:
Maximum Length of a Concatenated String with Unique Characters
SolveYou are given an array of strings arr. A string s is formed by the concatenation of a subsequence of arr that has unique characters.
Group Anagrams
SolveGiven an array of strings strs, group the anagrams together. You can return the answer in any order.
Binary Tree Level Order Traversal
SolveGiven the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level).
Minimum Path Sum
SolveGiven a m x n grid filled with non-negative numbers, find a path from top left to bottom right, which minimizes the sum of all numbers along its path.
Sliding Window Maximum
SolveYou are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see...
Min Stack
SolveDesign a stack that supports push, pop, top, and retrieving the minimum element in constant time.
Two Sum
SolveGiven an array of integers nums and an integer target, return the indices of the two numbers that add up to target.
Valid Parentheses
SolveGiven a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
Shortest Path in Binary Matrix
SolveGiven an n x n binary matrix grid, return the length of the shortest clear path in the matrix. If there is no clear path, return -1.
Word Break
SolveGiven a string s and a dictionary of strings wordDict, return true if s can be segmented into a space-separated sequence of one or more dictionary words.
Basic Calculator
SolveGiven a string s representing a valid expression, implement a basic calculator to evaluate it, and return the result of the evaluation.
Merge Sorted Array
SolveYou are given two integer arrays nums1 and nums2, sorted in non-decreasing order, and two integers m and n, representing the number of elements in nums1 and num...
Design HashMap
SolveDesign a HashMap without using any built-in hash table libraries.
Integer to Roman
SolveSeven different symbols represent Roman numerals with the following values:
Search in Rotated Sorted Array
SolveThere is an integer array nums sorted in ascending order (with distinct values).
Merge Two Sorted Lists
SolveYou are given the heads of two sorted linked lists list1 and list2.
Restore IP Addresses
SolveA valid IP address consists of exactly four integers separated by single dots. Each integer is between 0 and 255 (inclusive) and cannot have leading zeros.
Top K Frequent Words
SolveGiven an array of strings words and an integer k, return the k most frequent strings.
Longest Palindromic Substring
SolveGiven a string s, return the longest palindromic substring in s.
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent Palo Alto Networks interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
Palo Alto Networks interviews focus heavily on array, string, hash-table problems. If you're short on time, these are the categories to prioritize. The problems on this page are sorted by frequency, so start from the top and work your way down.
Beyond solving problems, practice explaining your approach. Palo Alto Networks interviewers care about your thought process - how you break down a problem, consider edge cases, and evaluate tradeoffs between solutions. A clean O(n) solution you can explain clearly beats an O(log n) solution you can't articulate.
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Palo Alto Networks has been reported to ask 25 distinct coding problems. The most common topics are array, string, hash-table. 5 are Easy difficulty, 17 are Medium, and 3 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 25 reported problems, Palo Alto Networks interviews are in line with industry averages - 12% Hard vs 18% overall. 68% of questions are Medium difficulty. Focus on the high-frequency Medium problems first, then work through the Hard ones.
Start with the highest-frequency problems listed on this page. Focus on the core topics: array, string, hash-table. Practice solving them under time pressure and explaining your approach out loud. Mock interviews with AI can simulate the real experience.
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