Algorithm Study

Adding two integers without the + or - operators using bitwise XOR, AND, and masking in Python

Finding grid coordinates that drain to both oceans using reverse DFS from ocean boundaries in Python

Finding the minimum window substring containing all target characters with two pointers and have/need counts in Python

Finding the contiguous subarray with the largest product using dynamic programming tracking both min and max in Python

Detecting a cycle in a singly-linked list using Floyd's two-pointer algorithm in Python

Counting palindromic substrings via odd and even expand-around-center checks in Python

Sliding window solution tracking maximum character frequency in Python

Computing the longest common subsequence of two strings with a 2D dynamic programming table in Python

Deep copying an undirected graph using a hash map and DFS recursion in Python

Reversing a 32-bit unsigned integer using bitwise shifts and masking in Python

A Python sliding-window solution using a set to maintain unique characters

An iterative Python solution that reverses next pointers in place with three references

A Python matrix simulation using direction vectors and in-place visit markers

An O(n²) Python DP solution that tracks the longest increasing subsequence ending at each index

A WordDictionary implementation using a Trie for storage and DFS for wildcard search

A Python two-pointer solution that moves the height limiting the current area

A Python stack solution that validates bracket type and closing order

Implementing a Trie with fixed 26-child nodes and an is_end marker

A Python dynamic programming solution for checking whether a string can be segmented by a word dictionary

Encoding and restoring a list of strings by recording each string's length and a delimiter

Grouping anagram strings by using each sorted string as the hash map key

A one-pass Python solution that tracks the lowest earlier price to calculate maximum profit

A Python DFS and memoization solution that stores the minimum coin count for each remaining amount

A Python DFS and backtracking solution that marks visited board cells in place

A Python binary search solution for the minimum value in a rotated sorted array

A Python DFS solution that compares the depths of the left and right subtrees

A Python solution that merges two sorted linked lists with a dummy node and moving pointers

A Python recursion and memoization solution that counts valid one-digit and two-digit decodings

A Python solution using Kadane's algorithm to find the maximum sum of a contiguous subarray

A Python backtracking solution to Combination Sum using a start index and pruning

A Python solution that counts 1 bits by repeatedly dividing by 2

A two-pointer Python solution for checking palindromes after normalizing alphanumeric characters

A DFS Python solution for checking whether a BST is built with valid value ranges

A 3Sum solution using sorting and a two-sum-style hash map approach.

A left-product and right-product solution for Product of Array Except Self.

A recursion and memoization write-up for the Climbing Stairs problem.

A comparison of sorting and character counting for the Valid Anagram problem.

Solving the rob-or-skip choice with top-down DP and memoization

Using a set to count each consecutive sequence only from its starting point

Using frequency counting and bucket arrays to return the top k frequent elements

Comparing brute force, two-pass hash map, and one-pass hash map approaches for Two Sum

Comparing brute force, sorting, and hash set approaches for duplicate detection

Solving BST range sum through BFS, DFS, and prefix sums

Why a modified Bellman-Ford approach fits the K-stop constraint better, and some implementation notes