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Articles in Java
Equal Point in Brackets
Find the optimal split point in bracket strings where opening brackets left equal closing brackets right. Efficient O(n) solution.
Find the Kth Missing Positive Number Using Binary Search
This article explains how to efficiently find the kth missing positive number in a sorted array. Using the insight that the number of missing numbers before an index i is arr[i] - (i+1), the problem can be solved with binary search, reducing time complexity from O(n + k) to O(log n). The article includes step-by-step examples and a clear Java implementation.
Number of Valid Parentheses – Catalan Number Pattern
Unlock the secret to counting valid parentheses! Discover the Catalan Number pattern and solve this common coding challenge efficiently.
Binary Searchable Count Count Binary Searchable Elements in an Unsorted Array
Discover which elements are discoverable via binary search on unsorted arrays. Learn the O(n) algorithm and its O(log n) space complexity.
Find a Peak Element in a 2D Matrix
This article explains how to find a peak element in a 2D matrix efficiently. A peak element is defined as an element that is greater than or equal to its four immediate neighbors (top, bottom, left, right). For edge and corner elements, missing neighbors are treated as negative infinity.
Count Elements Less Than or Equal to x in a Sorted Rotated Array
Learn how to efficiently count elements less than or equal to a given value in a sorted rotated array using binary search. Includes concept, pivot detection, and Java solution with O(log n) complexity.
Stock Span Problem – Monotonic Stack Pattern
Master the Stock Span Problem with the Monotonic Stack pattern. Efficiently find consecutive days with lower or equal stock prices in O(n) time.
Non-Attacking Black and White Knight Arrangements on an n × m Chessboard
Learn how to count the number of ways to place a black and white knight on an n x m chessboard so that they do not attack each other. Step-by-step explanation, formula derivation, and efficient Java solution included.
K-th Element of Two Sorted Arrays
Learn how to find the K-th element of two sorted arrays using binary search. Understand the partition-based approach, intuition, complexity analysis, and optimized Java solution with O(log(min(n, m))) time complexity.
XOR Pairs Less Than K
Learn how to count the number of pairs in an array whose XOR is less than a given number K using Trie-based optimization. Includes concept explanation, examples, and efficient Java solution.
Adding Two Numbers Represented by Linked Lists
Learn how to add two numbers represented by linked lists using an efficient O(n + m) approach. Understand the concept, reversing linked lists, carry handling, and Java solution with detailed explanation.
Brackets in Matrix Chain Multiplication
Learn how to solve the Matrix Chain Multiplication Brackets problem using Dynamic Programming. Understand the concept, optimal parenthesization, DP table construction, and Java implementation to print the minimum-cost multiplication order.
Remove K Digits Problem – Greedy Stack Approach to Find the Smallest Number
Learn how to solve the “Remove K Digits” problem using a greedy monotonic stack approach. This article explains how to efficiently remove k digits from a number string to form the smallest possible result while maintaining digit order, along with a Java implementation and clear intuition.
Count Subset With Target Sum II – Meet in the Middle Java Solution
Learn how to solve Count Subset With Target Sum II using the Meet in the Middle technique. Includes intuition, dry run, complexity analysis, and optimized Java code.
Expression Contains Redundant Bracket or Not – Java Stack Solution Explained
Learn how to detect redundant brackets in an expression using a stack. Includes intuition, dry run, complexity analysis, and optimized Java O(n) solution.
Candy Problem in Java – Greedy O(n) Time and O(1) Space Solution
earn how to solve the Candy problem using an optimal greedy algorithm. Includes intuition, dry run, complexity analysis, and Java solution with O(n) time and O(1) space.
Palindrome Pairs in an Array of Strings – Java Solution with HashMap
Learn how to solve the Palindrome Pairs problem using HashMap and palindrome prefix-suffix checking. Includes intuition, dry run, complexity analysis, and optimized Java code.
Lexicographically Smallest String After Removing K Characters Using a Monotonic Stack
Learn how to find the lexicographically smallest string after removing K characters using a monotonic stack in Java. Includes explanation, dry run, and optimized O(n) solution.
Next Element With Greater Frequency – Java O(n) Stack Solution
Learn how to solve the Next Element With Greater Frequency problem using HashMap and Monotonic Stack. Includes intuition, dry run, complexity analysis, and optimized Java solution.
Kth Largest in a Stream
Find the Kth largest element in a stream efficiently using a Min Heap. This approach optimizes for streaming data and top K element retrieval. O(n log k).
Buy Stock with Transaction Fee
Maximize stock-trading profit with a transaction fee using a two-state dynamic programming approach. Includes an O(n)-time, O(1)-space Java solution using hold and cash states.
Number of BSTs From Array
Calculate the number of unique Binary Search Trees (BSTs) possible for each element in an array as the root. Leverages Catalan numbers for efficient computation.
Opposite Sign Pair Reduction
Master the 'Opposite Sign Pair Reduction' problem! Learn how to efficiently reduce an array using a stack-based approach, simulating collisions. Includes Java code & complexity analysis.
Length of Longest Cycle in a Directed Graph
Learn how to find the length of the longest cycle in a directed graph where each node has at most one outgoing edge. This article explains the concept using a functional graph approach, combined with DFS and timestamp tracking to efficiently detect cycles and compute their lengths in O(V + E) time. Includes a clean Java implementation, step-by-step explanation, and edge case handling—ideal for coding interviews and advanced graph problem practice.
Remove Spaces from a String (Java)
Learn how to remove all spaces from a given string in Java while preserving the order of characters. This article explains a simple O(n) solution using StringBuilder, along with step-by-step logic and examples.
