LeetCode Challenge Series
Solving problems one step at a time — with interactive visualizations.
LeetCode #1: Two Sum
Brute force vs hash map optimization. Visualize the algorithm step-by-step.
Read solutionLeetCode #2: Add Two Numbers
Adding two numbers stored in reverse-linked lists with carry logic.
Read solutionLeetCode #3: Longest Substring Without Repeating Characters
Using the sliding window technique to find the longest unique substring.
Read solutionLeetCode #4: Median of Two Sorted Arrays
Finding the median of two sorted arrays in logarithmic time using binary search on partitions.
Read solutionLeetCode #5: Longest Palindromic Substring
Finding the longest palindrome in a string using the expand-around-center technique.
Read solutionLeetCode #6: Zigzag Conversion
Convert a string into a zigzag pattern and read row-by-row — a classic simulation problem with real cipher applications.
Read solutionLeetCode #7: Reverse Integer
Reverse the digits of an integer safely — with overflow protection and digit-by-digit animation.
Read solutionLeetCode #8: String to Integer (atoi)
Convert a string to an integer safely — with whitespace, signs, overflow, and real-world parsing logic.
Read solutionLeetCode #9: Palindrome Number
Check if a number reads the same forwards and backwards — with math, not strings.
Read solutionLeetCode #10: Regular Expression Matching
From simple recursion to dynamic programming — build a regex engine step by step.
Read solutionLeetCode #11: Container With Most Water
Find the container that holds the most water using the two-pointer technique — with an interactive height chart.
Read solutionLeetCode #12: Integer to Roman
Convert an integer to a Roman numeral using greedy matching — with a step-by-step visual builder.
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