LeetCode

LeetCode problems' solutions for coding interview preparation.

Amount of problems solved: 103/143

Paid Problems (7)

• Encode and Decode Strings
• Meeting Rooms
• Meeting Rooms II
• Alien Dictionary
• Walls and Gates
• Graph Valid Tree
• Number of Connected Components In An Undirected Graph

Solved Problems

• Arrays & Hashing
  • Easy
    • Contains Duplicate
    • Valid Anagram
    • Two Sum
  • Medium
    • Group Anagrams
    • Top K Frequent Elements
    • Valid Sudoku
    • Product of Array Except Self
    • Longest Consecutive Sequence
  • Hard
• Two Pointers
  • Easy
    • Valid Palindrome
  • Medium
    • Two Sum II Input Array Is Sorted
    • Container With Most Water
    • 3Sum
  • Hard
• Sliding Window
  • Easy
    • Best Time to Buy and Sell Stock
  • Medium
    • Longest Substring Without Repeating Characters
    • Permutation in String
  • Hard
• Stack
  • Easy
    • Valid Parentheses
  • Medium
    • Generate Parentheses
    • Min Stack
    • Evaluate Reverse Polish Notation
    • Daily Temperatures
    • Car Fleet
  • Hard
• Binary Search
  • Easy
    • Binary Search
  • Medium
    • Coco Eating Bananas
    • Search a 2D Matrix
    • Find Minimum in Rotated Sorted Array
    • Search in Rotated Sorted Array
    • Time Based Key-Value Store
  • Hard
• Linked List
  • Easy
    • Reverse Linked List
    • Merge Two Sorted Lists
    • Linked List Cycle
  • Medium
    • Remove Nth Node From End of List
    • Add Two Numbers
    • Copy List with Random Pointer
    • LRU Cache
    • Reorder List
    • Find The Duplicate Number
  • Hard
    • Merge K Sorted Lists
    • Reverse Nodes in k-Group
• Trees
  • Easy
    • Maximum Depth of Binary Tree
    • Invert Binary Tree
    • Same Tree
    • Diameter of a Binary Tree
    • Balanced Binary Tree
    • Subtree of Another Tree
  • Medium
    • Binary Tree Level Order Traversal
    • Binary Tree Right Side View
    • Count Good Nodes in Binary Tree
    • Kth Smallest Element in a BST
    • Lowest Common Ancestor of a Binary Search Tree
    • Validate Binary Search Tree
    • Construct Binary Tree from Preorder and Inorder Traversal
  • Hard
    • Binary Tree Maximum Path Sum
    • Serialize and Deserialize Binary Tree
• Heap/Priority Queue
  • Easy
    • Kth Largest Element in a Stream
    • Last Stone Weight
  • Medium
    • K Closest Points to Origin
    • Kth Largest Element in an Array
    • Design Twitter
    • Task Scheduler
  • Hard
    • Find Median from Data Stream
• Backtracking
  • Easy
  • Medium
    • Subsets
    • Subsets II
    • Combination Sum
    • Permutations
  • Hard
• Tries
  • Easy
  • Medium
  • Implement Trie (Prefix Tree)
  • Design Add and Search Words Data Structure
  • Hard
• Graphs
  • Easy
  • Medium
    • Number of Islands
    • Max Area of Island
    • Course Schedule
    • Course Schedule II
    • Redundant Connection
    • Rotting Oranges
    • Surrounded Regions
    • Clone Graph
  • Hard
    • Word Ladder
• Advanced Graphs
  • Easy
  • Medium
    • Min Cost to Connect All Points
    • Network Delay Time
    • Cheapest Flights Within K Stops
  • Hard
• 1D Dynamic Programming
  • Easy
    • Climbing Stairs
    • Min Cost Climbing Stairs
  • Medium
    • House Robber
    • House Robber II
    • Longest Palindromic Substring
    • Palindromic Substrings
    • Decode Ways
    • Partition Equal Subset Sum
    • Coin Change
    • Maximum Product Subarray
    • Word Break
  • Hard
• 2D Dynamic Programming
  • Easy
  • Medium
    • Unique Paths
  • Hard
• Greedy
  • Easy
  • Medium
    • Maximum Subarray
    • Jump Game
  • Hard
• Intervals
  • Easy
  • Medium
    • Insert Interval
  • Hard
• Math & Geometry
  • Easy
    • Happy Number
    • Plus One
  • Medium
    • Rotate Image
    • Pow(x, n)
  • Hard
• Bit Manipulation
  • Easy
    • Single Number
    • Number of 1 Bits
    • Counting Bits
    • Reverse Bits
    • Missing Number
  • Medium
  • Hard

Useful Tricks and Techniques

• Slow Pointer and Fast Pointer
• Linked List Reversal
• Doubly Linked List
• Dictionaries that stores key-value pairs where the value is a ListNode or a TreeNode
• Concept of Deep Copy
• Two Pointers
• Sliding Window
• LIFO -> Probably a Stack
• FIFO -> Probably a Queue
• Queue where elements have priorities -> Heap
• Learn more about Floyd's Cycle-Detection Algorithm in an Array/Linked List.
• Remember how to validate a BST: range update while doing a DFS traversal.
• Remember how to calculate the LCA of a BST (The code is very very simple).
• Remember how to solve the problem "Binary Tree Maximum Sum" (Has a lot of corner and tricky cases).
• See the NeetCode solution for "Design Twitter".
• See the NeetCode solution for "Task Scheduler".
• Solve the "Find Minimum in Rotated Sorted Array" again.
• In Binary Search problems, think very carefully about whether you need to use < or <=.
• The "Median of Two Sorted Arrays" problem is very hard and full of tricks.
• The "3Sum" problem is very interesting.
• In the problem "Permutation in String", the left pointer always decrements the freqDict and the right pointer always increments the freqDict.
• The "Design Add and Search Words Data Structure" problem is very interesting and tricky. It's a good idea to do it one more time.
• The "Jump Game" problem is an excelent greedy problem.
• The "Maximum Product Subarray" problem is a tricky 1D DP problem worth reviewing.
• The "Word Break" problem is a very good 1D DP problem.