Small Problems & their Solution in Java

Problems

Basic

• FizzBuzz
• Training Times
• The next number
• Searching 101
• Push Ups with Blaze
• Problem : x1

String Manipulation

• One Loop Design: print a star symbol in one loop
• Longest substring without repeating characters (micro1)
• Anything you can do, I can do better
• Valid Identifier Checker
• Diamond Printer
• Reverse a String
• Check if a vowel exists in a String
• Check for palindrome
• Remove whitespaces
• Remove leading & trailing spaces
• Print all unique words, excluding the same words
• Find the duplicate characters in a string
• Sort String Sequences
• Write a program to find out how many times two given characters appear in any text file.
• Remove all occurrences of a character in a String

Dates

• Using Java 8 date-time library in CLASSPATH (package private) file, write a program that shows how you can add time to any time with respect to midnight on Jan. 1, 2000.
• Specify date format

Bit Manipulation

• Bits Manipulation formulas
• Check if a number is a power of 2
• Hamming Weight implementation (return 1-bits of a binary representation of a number)
• Binary to Decimal Converter
• Reverse bits

Algorithms

• Shortest path in Alabama - Dijkstra
• Verifying the 8-Queens
• Implement Binary Search

Mathematics

• Print the Fibonacci sequence
• Factorial
• Maths formulas
• Find the least amount of coins needed for an amount
• Circle Intersection
• Swap two numbers using the third variable
• Swap two numbers without using the third variable
• Prime number finder
• Power

Data Structures

Arrays

• Find the first duplicate in an array
• Write a program to sort a sequence of numbers in ascending order.
• Missing number
• Sum all elements in an array
• Shuffle an array
• Find the second-largest number in an array

Lists

• Check for odd numbers in a list
• Merge two lists

Linked Lists

• Find the middle element of a linked list

Stack

• Implement a stack using two queues
• Stack Machine Interpretation

HashMap

• Implement a cache using a HashMap

Multithreading

• Solve the producer-consumer problem using multithreading
• Illustrate a deadlock scenario

Advanced

• Java: Tricky Interview Problems
• Guess the Output
• Guess the Output - Tilde Bits
• Find the mistakes in a code snippet

To Do

• The rest of Digital Ocean's problems

  • Implement Merge Sort
  • Compare two arrays' elements
  • Sort HashMap by value
  • Get distinct chars & their count
  • Prove that String is immutable programmatically
  • Showcase inheritance
  • How do you show a diamond problem with multiple inheritance in Java?
  • Illustrate try-catch
  • Illustrate NPE
  • Create a Record
  • Textblocks
  • Multilabel switch-case
  • Write an interface with default & static method
  • Create a functional interface
  • Illustrate lambda functions
  • Illustrate overriding & overloading

• Arrays

  • Two Sum
  • Best Time to Buy and Sell Stock
  • Contains Duplicate
  • Product of Array Except Self
  • Maximum Subarray
  • Maximum Product Subarray
  • Find Minimum in Rotated Sorted Array
  • Search in Rotated Sorted Array
  • 3Sum
  • Container With Most Water

• Dynamic Programming

  • Knapsack
  • Stairs
  • Longest Increasing Subsequence
  • Longest Common Subsequence
  • Word Break
  • Combination Sum
  • House Robber I
  • House Robber II
  • Decode Ways
  • Unique Paths
  • Jump Game

• Graphs

  • Given a list of edges and tasked to build your own graph from the edges
  • Implement BFS
  • Implement DFS
  • Implement Dijkstra’s algorithm
  • Implement Topological sort
  • Implement Bellman-Ford algorithm
  • Implement Floyd-Warshall algorithm
  • Implement Prim’s algorithm
  • Implement Kruskal’s algorithm
  • Clone graph
  • Course Schedule
  • Alien Dictionary
  • Pacific Atlantic Water Flow
  • Number of Islands
  • Graph Valid Tree
  • Number of Connected Components in an Undirected Graph
  • Longest Consecutive Sequence

• LinkedLists

  • Reverse a LL
  • Detect Cycle
  • Merge 2 Sorted
  • Merge k Sorted
  • Remove n-th node from end of list
  • Reorder list

• Maths

  • Square Root
  • Int to English

• Matrix

  • Set Matrix Zeroes
  • Spiral Matrix
  • Rotate Image
  • Word Search

• Strings

  • Rabin Karp
  • KMP
  • Valid Anagram
  • Valid Parentheses
  • Valid Palindrome
  • Longest Palindromic Substring
  • Palindromic Substrings

• Tree

  • Maximum Depth of Binary Tree
  • Same Tree
  • Invert or Flip Binary Tree
  • Binary Tree Maximum Path Sum
  • Binary Tree Level Order Traversal
  • Serialize and Deserialize Binary Tree
  • Subtree of Another Tree
  • Construct Binary Tree from Preorder and Inorder Traversal
  • Validate Binary Search Tree
  • Kth Smallest Element in a BST
  • Lowest Common Ancestor of BST

• Heaps

  • Merge K Sorted Lists
  • Top K Frequent Elements
  • Find Median from Data Stream

• Multithreading & Concurrency

  • Implement a thread-safe singleton class.
  • Write a program to demonstrate the use of synchronized blocks to achieve thread safety.
  • Implement a producer-consumer problem using wait() and notify() methods.
  • Java’s ExecutorService to execute a list of tasks concurrently.
  • Implement a thread-safe cache using ConcurrentHashMap.
  • Write a program to demonstrate the use of atomic variables for thread-safe operations.
  • Implement a deadlock scenario and explain how to avoid it.
  • Use Java’s Lock interface to implement a custom lock for thread synchronization.
  • Implement a thread-safe queue using BlockingQueue.
  • Write a program to demonstrate the use of CompletableFuture for asynchronous programming.

Sources

1. Tausig's Easy Problems
2. Digital Ocean's Interview Questions
3. Indeed's Java Interview Problems
4. Coding Interviews for Dummies