Top 20 Data Structures Interview Questions to Master for FAANG Success Quiz

Sharpen your data structures and algorithms knowledge with these essential FAANG interview questions, covering array operations, strings, dynamic programming, and optimization strategies.

1. Single Number in an Array

   Given an array where every element appears twice except for one, which operation can be used to efficiently find the single unique number?

   1. Array Sorting
   2. Bitwise XOR
   3. Mathematical Summation
   4. Hash Map Counting

   Explanation: Bitwise XOR uniquely identifies the single number in linear time and constant space, as duplicates cancel each other out. Sorting has higher time complexity, hash map counting uses extra space, and mathematical summation is unreliable if numbers are negative or repeated with varying values.

2. Valid Palindrome Check

   What is the best approach to determine if a string is a valid palindrome, considering only alphanumeric characters and ignoring cases?

   1. Reverse the string and compare
   2. Count character frequencies
   3. Convert to ASCII values and sum
   4. Use two pointers from ends moving inward

   Explanation: Two pointers efficiently compare the relevant characters from both ends while skipping non-alphanumeric characters. Reversing and comparing requires more space, counting frequencies does not validate palindromes, and converting to ASCII values can't determine character order.

3. Best Time to Buy and Sell Stock

   Given an array of daily stock prices, what is the optimal method to compute the maximum profit from a single buy-and-sell transaction?

   1. Sort the prices and subtract the smallest from the largest
   2. Track the minimum price and update maximum profit accordingly
   3. Calculate the sum of all price differences
   4. Use a stack to find local minimum and maximum

   Explanation: Tracking the minimum price seen so far and updating the maximum profit ensures a single transaction and linear time. Sorting disrupts order and isn't appropriate, summing differences allows multiple transactions, and a stack approach complicates simplicity without extra benefit.

4. Longest Common Prefix

   What is an efficient way to find the longest common prefix among an array of strings?

   1. Sort the array and pick the first string
   2. Concatenate all strings and search for the shortest substring
   3. Use a hash map to track character frequencies
   4. Compare characters one-by-one for each string until a mismatch is found

   Explanation: Comparing characters synchronously across strings finds the common prefix efficiently. Concatenation does not preserve word boundaries, hash maps track frequencies but not position, and simply picking the first string ignores comparisons entirely.

5. Intersection of Two Arrays

   To find all distinct elements common to two unsorted arrays, which data structure ensures efficient look-up and minimal time complexity?

   1. Array Sorting
   2. Stack
   3. Linked List
   4. Hash Set

   Explanation: A hash set provides constant-time look-up for elements and eliminates duplicates, making it ideal for computing intersections. Sorting can increase complexity, stacks are unsuitable for unordered access, and linked lists do not provide efficient membership checks.