Two Sum is the most asked interview problem at Google, Amazon and Meta. Learn every approach from O(n²) brute force to O(n) HashMap with C, C++, Java, JavaScript and Python solutions.
Kadane's Algorithm is a must-know pattern for FAANG interviews. Solve Maximum Subarray in O(n) time with full solutions in C, C++, Java, JavaScript and Python, plus divide-and-conquer O(n log n) alternative.
Move all zeroes to end while maintaining relative order of non-zero elements. Optimal O(n) two-pointer solution with minimal writes. Full C, C++, Java, JavaScript and Python code.
Merge two sorted arrays in-place by filling from the end. The classic 3-pointer technique asked at Meta and Microsoft. Full solutions in C, C++, Java, JavaScript and Python.
Find the element that appears once while every other appears twice. The XOR bit trick gives O(n) time and O(1) space. Full solutions in C, C++, Java, JavaScript, Python plus Single Number II and III extensions.
Determine if a string is a palindrome considering only alphanumeric characters and ignoring cases. Two pointer O(n) O(1) solution with all 5 language implementations.
Find all unique triplets summing to zero. Sort array then fix one element and use two pointers. Full O(n²) solution in C, C++, Java, JavaScript and Python.
Find two lines that together with the x-axis form a container holding the most water. Greedy two-pointer O(n) — never check a pair that can't be optimal.
Search a target in a rotated sorted array with no duplicates. Modified binary search identifies which half is sorted, then checks the target range. O(log n) time.
High-frequency string problems from Meta and Google interviews: valid parentheses, longest substring without repeating characters, zigzag conversion, and string to integer.
Full company-specific mock sessions. Each simulation replicates the actual interview format, problem difficulty distribution, and evaluation criteria of Google, Meta, and Amazon.
Strategic guide to company-specific DSA preparation: Google's focus on graphs and DP, Meta's emphasis on arrays and trees, Amazon's leadership principles alignment with system design and BFS.
Serialize a binary tree to a string and deserialize it back. Meta loves this problem for testing tree traversal and string parsing. Both BFS and preorder DFS approaches shown.
Implement a read() function using a read4() primitive. Two variants: read once and read multiple times. Tests buffer management and pointer arithmetic.
Create a deep copy of an undirected graph using DFS with a HashMap to track visited/cloned nodes. Meta tests this to evaluate graph traversal and pointer manipulation.
Complete recap of all 24 company-tagged problems with pattern classification, company attribution, and key insights. Use as a final review checklist before company-specific interviews.