LeetCodeNet

LeetCode problems with clean code, detailed explanations and different easy-understandable solutions. All problems are grouped by patterns, so you can train in solving of specific type of problems.

Level: Easy

Pattern: without

#9: Palindrome Number (Math)
#13: Roman to Integer (Math)
#20: Valid Parentheses (String)
#21: Merge Two Sorted Lists (Linked List)
#66: Plus One (Array)
#118: Pascal's Triangle (DP)
#155: Min Stack (DP)
#202: Happy Number (Math)
#206: Reverse Linked List (Linked list)
#225: Implement Stack using Queues (Design)
#232: Implement Queue using Stacks (Design)
#237: Delete Node in a Linked List (Linked list)
#303: Range Sum Query - Immutable (Design)
#412: FizzBuzz (Math, Design)
#414: Third Maximum Number (Array)
#485: Max Consecutive Ones (Array)
#566: Reshape the Matrix (Array)
#844: Backspace String Compare (Array, Stack)
#867: Transpose Matrix (Array)
#976: Largest Perimeter Triangle (Math)
#1232: Check If It Is a Straight Line (Math)
#1281: Subtract the Product and Sum of Digits of an Integer (Math)
#1295: Find Numbers with Even Number of Digits (Math, Array)
#1299: Replace Elements with Greatest Element on Right Side (Array)
#1431: Kids With the Greatest Number of Candies (Array)
#1502: Can Make Arithmetic Progression From Sequence (Math, Array)
#1523: Count Odd Numbers in an Interval Range (Array)
#1539^ Kth missing positive number (Array)
#1572: Matrix Diagonal Sum (Array)
#1588: Sum of All Odd Length Subarrays (Array)
#1603: Design Parking System (Design)
#1672: Richest Customer Wealth (Array)
#1678: Goal Parser Interpretation (String)
#1732: Find the Highest Altitude (Array)
#1768: Merge Strings Alternately (String)
#1822: Sign of the Product of an Array (Math)
#1974: Minimum Time to Type Word Using Special Typewriter (String)
#2643: Row With Maximum Ones (Array)
#2660: Determine the Winner of a Bowling Game (Array)
#2716: Minimize String Length (String)
#2733: Neither Minimum nor Maximum (Array)
#2739: Total Distance Traveled (Math)

Pattern: Sorting

#14: Longest Common Prefix (String)
#217: Contains Duplicate (Array)
#448: Find All Numbers Disappeared in an Array (Array)
#1046: Last Stone Weight (Array, PriorityQueue)
#1051: Height Checker (Array, Bucket)
#1491: Average Salary Excluding the Minimum and Maximum Salary (Array)

Pattern: Prefix sum

#724: Find Pivot Index (Array)
#1480: Running Sum of 1d Array (Array)
#2670: Find the Distinct Difference Array (Array)

Pattern: Breadth-First search (BFS)

#104: Maximum Depth of Binary Tree (Tree)
#112: Path Sum (Tree)
#144: Binary Tree Preorder Traversal (Tree)
#145: Binary Tree Postorder Traversal (Tree)
#226: Invert Binary Tree (Tree)
#404: Sum of Left Leaves (Tree)
#617: Merge Two Binary Trees (Tree)
#637: Average of Levels in Binary Tree (Tree)
#733: Flood Fill (Array)

Pattern: Depth-First search (DFS)

#94: Binary Tree Inorder Traversal (Tree)
#101: Symmetric Tree (Tree)
#589: N-ary Tree Preorder Traversal (Tree)

Pattern: Binary tree

#235: Lowest Common Ancestor of a Binary Search Tree (Tree)
#700: Search in a Binary Search Tree (Tree)

Pattern: Two pointers

#26: Remove Duplicates from Sorted Array (Array)
#27: Remove Element (Array)
#83: Remove Duplicates from Sorted List (Linked List)
#125: Valid Palindrome (String)
#169: Majority Element (Array)
#203: Remove Linked List Elements (Linked List)
#283: Move Zeroes (Array)
#344: Reverse String (String)
#345: Reverse Vowels of a String (String)
#387: First Unique Character in a String (String)
#350: Intersection of Two Arrays II (Array)
#392: Is Subsequence (String)
#557: Reverse Words in a String III (String)
#696: Count Binary Substrings (String)
#905: Sort Array By Parity (Array)
#941: Valid Mountain Array (Array)
#977: Squares of a Sorted Array (Array)
#1089: Duplicate Zeroes (Array)
#1790: Check if One String Swap Can Make Strings Equal (String)
#2697: Lexicographically Smallest Palindrome (String)
#2717: Semi-Ordered Permutation (Array)

Pattern: Two pointers: slow/fast

#141: Linked List Cycle (Linked List)
#234: Palindrome Linked List (Linked List)
#876: Middle of the LInked List (Linked List)

Pattern: Hash table

#1: Two Sum (Array)
#205: Isomorphic Strings (String)
#242: Valid Anagram (String)
#350: Intersection of Two Arrays II (Array)
#383: Ransom note (String)
#389: Find the Difference (String)
#409: Longest Palindrome (String)
#705: Design HashSet (Design)
#706: Design HashMap (Design)
#953: Verifying an Alien Dictionary (String)
#1346: Check If N and Its Double Exist (Array)
#1394: Find Lucky Integer in an Array (Array)
#2049: Finding 3-Digit Even Numbers (Array)

Pattern: Monotonic stack

#496: Next Greater Element I (Array)

Pattern: Char manipulation

#709: To Lower Case (String)
#1309: Decrypt String from Alphabet to Integer Mapping (String)
#1844: Replace All Digits with Characters (String)

Pattern: Bit manipulation

#136: Single number (Array)
#190: Reverse bits (Bits)
#191: Number of 1 Bits (Bits)
#231: Power of Two (Bits)
#268: Missing Number (Array)
#461: Hamming Distance (Bits)
#1290: Convert Binary Number in a Linked List to Integer (Linked List)
#1342: Number of Steps to Reduce a Number to Zero (Bits)
#1356: Sort Integers by The Number of 1 Bits (Array)

Pattern: KMP algorithm

#28: Implement strStr (String)

Pattern: Divide and conquer

#108: Convert Sorted Array to Binary Search Tree (Tree)

Pattern: Binary search

#35: Search Insert Position (Array)
#69: Sqrt(x) (Math)
#278: First Bad Version (Array)
#367: Valid Perfect Square (Math)
#374: Guess Number Higher or Lower (Array)
#653: Two Sum IV - Input is a BST (Tree)
#704: Binary Search (Array)
#744: Find Smallest Letter Greater Than Target (Array)
#1337: The K Weakest Rows in a Matrix (Array)
#1351: Count Negative Numbers in a Sorted Matrix (Array)
#1385: Find the Distance Value Between Two Arrays (Array)
#1608: Special Array With X Elements Greater Than or Equal X (Array)

Pattern: Dynamic programming

#70: Climbing stairs (Bottom-up)
#746: Min Cost Climbing Stairs (Bottom-up)
#509: Fibonacci Number (Bottom-up)
#605: Can Place Flowers (Bottom-up)

Pattern: Kadane's algorithm

#121: Best Time to Buy and Sell Stock (DP)

Pattern: Greedy

#2696: Minimum String Length After Removing Substrings (String)

Level: Medium

Pattern: without

#2: Add Two Numbers (Linked list)
#7: Reverse Integer (Math)
#38: Count and say (String)
#54: Spiral Matrix (Array)
#71: Simplify Path (String)
#382: Linked List Random Node (Linked list, Design)
#394: Decode String (String, Stack)
#848: Shifting Letters (String)
#1328: Break a Palindrome (String)
#1472: Design Browser History (Linked List, Design)
#1980: Find Unique Binary String (Array)
#2348: Number of Zero-Filled Subarrays (Math, Array)
#2671: Frequency Tracker (Design)
#2672: Number of Adjacent Elements With the Same Color (Array)
#2718: Sum of Matrix After Queries (Array)
#2734: Lexicographically Smallest String After Substring Operation (String)

Pattern: Sorting

#347: Top K Frequent Elements (Array)
#692: Top K Frequent Words (Array, Bucket)
#2300: Successful Pairs of Spells and Potions (Array)
#2740: Find the Value of the Partition (Array)

Pattern: Binary search

#33: Search in Rotated Sorted Array (Array)
#34: Find First and Last Position of Element in Sorted Array (Array)
#74: Search a 2D Matrix (Array)
#153: Find Minimum in Rotated Sorted Array (Array)
#852: Peak Index in a Mountain Array (Array)

Pattern: Two pointers

#5: Longest Palindromic Substring (String)
#88: Merge Sorted Array (Array)
#142: Linked List Cycle II (Linked List)
#167: Two Sum II - Input Array Is Sorted (Array)
#633: Sum of Square Numbers (Math)
#881: Boats to Save People (Array)
#946: Validate Stack Sequences (Array)
#1004: Max Consecutive Ones III (Array)
#1855: Maximum Distance Between a Pair of Values (Array)
#2390: Removing Stars From a String (String)

Pattern: Two pointers: slow/fast

#109: Convert Sorted List to Binary Search Tree (Tree, Linked list)

Pattern: Hash table

#299: Bulls and Cows (Array)
#2661: First Completely Painted Row or Column (Array)

Pattern: Sliding window

#3: Longest Substring Without Repeating Characters (String)
#424: Longest Repeating Character Replacement (String)
#438: Find All Anagrams in a String (String)
#567: Permutation in String (String)
#1456: Maximum Number of Vowels in a Substring of Given Length (String)

Pattern: Prefix sum

#2439: Minimize Maximum of Array (Array)

Pattern: Kadane's algorithm

#53: Maximum Subarray (Array)

Pattern: Backtracking

#46: Permutations (Array)
#211: Design Add and Search Words Data Structure (Prefix Tree, Design)
#784: Letter Case Permutation (String)
#2698: Find the Punishment Number of an Integer (Math)

Pattern: Binary tree

#98: Validate Binary Search Tree (Tree)

Pattern: Breadth-First search (BFS)

#102: Binary Tree Level Order Traversal (Tree)
#133: Clone Graph (Graph)
#958: Check Completeness of a Binary Tree (Tree)
#1466: Reorder Routes to Make All Paths Lead to the City Zero (Graph)
#2583: Kth Largest Sum in a Binary Tree (Tree)

Pattern: Depth-First search (DFS)

#129: Sum Root to Leaf Numbers (Tree)
#200: Number of Islands (Array)
#207: Course Schedule (Tree, Topological sort)
#994: Rotting Oranges (Array)
#1020: Number of Enclaves (Array)

Pattern: Bit manipulation

#2405: Optimal Partition of String (String)

Pattern: Prefix Tree

#208: Implement Trie (Design)

Pattern: Dynamic programming

#62: Unique Paths (Bottom-up, Array)
#63: Minimum Path Sum (Bottom-up, Array)
#516: Longest Palindromic Subsequence (Bottom-up, String)
#983: Minimum Cost For Tickets (Bottom-up, Array)

Pattern: Union-Find

#1319: Number of Operations to Make Network Connected (Graph)
#2316: Count Unreachable Pairs of Nodes in an Undirected Graph (Graph)

Level: Hard

Pattern: without

#23: Merge k Sorted Lists (Linked list)

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LeetCodeNet

Level: Easy

Pattern: without

Pattern: Sorting

Pattern: Prefix sum

Pattern: Breadth-First search (BFS)

Pattern: Depth-First search (DFS)

Pattern: Binary tree

Pattern: Two pointers

Pattern: Two pointers: slow/fast

Pattern: Hash table

Pattern: Monotonic stack

Pattern: Char manipulation

Pattern: Bit manipulation

Pattern: KMP algorithm

Pattern: Divide and conquer

Pattern: Binary search

Pattern: Dynamic programming

Pattern: Kadane's algorithm

Pattern: Greedy

Level: Medium

Pattern: without

Pattern: Sorting

Pattern: Binary search

Pattern: Two pointers

Pattern: Two pointers: slow/fast

Pattern: Hash table

Pattern: Sliding window

Pattern: Prefix sum

Pattern: Kadane's algorithm

Pattern: Backtracking

Pattern: Binary tree

Pattern: Breadth-First search (BFS)

Pattern: Depth-First search (DFS)

Pattern: Bit manipulation

Pattern: Prefix Tree

Pattern: Dynamic programming

Pattern: Union-Find

Level: Hard

Pattern: without