Knowledge Guide

DSA Problem Ladders

Every problem in the guide, grouped by pattern and laddered easy → hard — a routed path instead of a pile. ★ marks the canonical interview must-dos. Toggle ★ Core for a fast-track set, filter by difficulty, and check off what you finish (saved in your browser).

549 problems · 115 ★core

▶Arrays11 · ★2

MBest Time to Buy and Sell MH-Index ★MJump Game ★MJump Game II MKids With the Greatest Number of Candies MProblem 1 Running Sum of 1d Array MProblem 2 Contains Duplicate MProblem 3 Left and Right Sum Differences MProblem 4 Find the Highest Altitude MRoman to Integer MZigzag Conversion

▶Hashing14 · ★3

MContains Duplicate II MDetermine if Two Strings Are Close ★MGroup Anagrams ★MLongest Consecutive Sequence MProblem 1 Counting Elements MProblem 1 First Non-repeating Character MProblem 2 Jewels and Stones MProblem 2 Largest Unique Number MProblem 3 Maximum Number of Balloons MProblem 3 Unique Number of Occurrences MProblem 4 Longest Palindrome ★MProblem 4 Longest Substring Without Repeating Characters MProblem 5 Ransom Note MWord Pattern

▶Two Pointers4 · ★0

MComparing Strings containing Backspaces MDutch National Flag Problem MMinimum Window Sort MPair with Target Sum

▶Sliding Window6 · ★1

MLongest Subarray of 1's After Deleting One Element ★MLongest Substring Without Repeating Characters MMax Consecutive Ones III MMaximum Average Subarray I MMaximum Number of Vowels in a Substring of Given Length MMinimum Size Subarray Sum

▶Stack13 · ★1

MDaily Temperatures MEvaluate Reverse Polish Notation MProblem 1 Balanced Parentheses MProblem 2 Reverse a String MProblem 3 Decimal to Binary Conversion MProblem 4 Next Greater Element MProblem 5 Sorting a Stack MProblem 6 Simplify Path MProblem 7 Remove All Adjacent Duplicates In String MProblem 8 Removing Stars From a String MProblem 9 Make The String Great MSimplify Path ★MValid Parentheses

▶Queues5 · ★0

MImplement Stack using Queues MMax of All Subarrays of Size 'k' MPalindrome Check using Queue MReverse a Queue MZigzag Iterator

▶Searching6 · ★0

MFrequency of the Most Frequent Element MMaximum Count of Positive Integer and Negative Integer MMinimize the Maximum of Two Arrays MMinimum Common Value MSearch a 2D Matrix II MSqrt

▶Sorting7 · ★2

MApple Redistribution into Boxes MDivide Array Into Arrays With Max Difference ★MMeeting Rooms II MReduction Operations to Make the Array Elements Equal MSort Array by Increasing Frequency MSort Vowels in a String ★MTop 'K' Frequent Numbers

▶Linked List9 · ★3

MAdd Two Numbers MOdd Even Linked List ★MProblem 1 Reverse Linked List MProblem 2 Remove Duplicates from Sorted List ★MProblem 3 Merge Two Sorted Lists MProblem 4 Find if Doubly Linked List is a Palindrome MProblem 5 Swap Nodes in Pairs ★MReverse Linked List II MReverse Nodes in k-Group

▶Trees72 · ★13

MAll Nodes Distance K in Binary Tree MAll Nodes Distance K in Binary Tree MAll Paths for a Sum MAmount of Time for Binary Tree to Be Infected MBalanced Binary Tree MBalanced Binary Tree MBinary Tree Path Sum MBinary Tree Paths MBottom View Of the Binary Tree MBoundary of Binary Tree MCheck if all leaves are at same level ★MClosest Binary Search Tree Value ★MConnect All Level Order Siblings ★MConnect Level Order Siblings MCount Good Nodes in Binary Tree MCount Good Nodes in Binary Tree MCount Paths for a Sum MCousins in Binary Tree MCreate Binary Tree From Descriptions MDeepest Leaves Sum MDelete Leaves With a Given Value MEven Odd Tree MEven Odd Tree MFind Largest Value in Each Tree Row MFind Largest Value in Each Tree Row MFind maximum depth of subtree MInsufficient Nodes in Root to Leaf Paths MIsomorphic Trees ★MKth Smallest Element in a BST ★MKth Smallest Element in a BST MLeaf-Similar Trees ★MLevel Order Successor ★MLowest Common Ancestor of a Binary Search Tree MMaximum Depth (or Height) of Binary Tree MMaximum Depth of N-ary Tree MMaximum Depth or Height of Binary Tree MMaximum Depth or Height of Binary Tree MMaximum Difference Between Node and Ancestor MMaximum Difference Between Node and Ancestor MMaximum Level Sum of a Binary Tree MMaximum Width of Binary Tree MMerge Two Binary Trees MMinimum Depth of a Binary Tree MMinimum Difference Between BST Nodes MMirror Image Trees ★MN-ary Tree Level Order Traversal MPath Sum III MPath Sum III MPath With Given Sequence MPath with Maximum Sum MPseudo-Palindromic Paths in a Binary Tree MPseudo-Palindromic Paths in a Binary Tree MRange Sum of BST ★MReverse Level Order Traversal MRight View of a Binary Tree MRight View of a Binary Tree ★MSerialize and Deserialize BST ★MSerialize and Deserialize N-ary Tree MSmallest String Starting From Leaf MSubtree of Another Tree MSum of Left Leaves MSum of Nodes with Even-Valued Grandparent MSum of Path Numbers MSum of Root To Leaf Binary Numbers MSymmetric Tree MTop View Of the Binary Tree MTree Diameter MTree Diameter ★MValidate Binary Search Tree ★MValidate Binary Search Tree MVerify Preorder Serialization of a Binary Tree MZigzag Traversal

▶Trie8 · ★2

MDesign Add and Search Words Data Structure MDesign Add and Search Words Data Structure MExtra Characters in a String ★MImplement Trie (Prefix Tree) ★MImplement Trie Prefix Tree MIndex Pairs of a String MSearch Suggestions System MSearch Suggestions System

▶Heap9 · ★2

MFind the Median of a Number Stream ★MK-th Smallest Prime Fraction ★MMedian of Two Sorted Arrays MMinimum Cost to Connect Sticks MRearrange String MSmallest Range Covering Elements from K Lists MSort Characters By Frequency MSort Characters By Frequency MTake Gifts From the Richest Pile

▶Recursion19 · ★1

MSolution Basic Sum ★MSolution Binary Search MSolution BST Inorder Traversal MSolution Check Prime MSolution Converting Decimal to Binary MSolution Depth First Search MSolution Factorial MSolution Fibonacci Series Using Memoization MSolution Good Number MSolution Greatest Common Divisor GCD MSolution Inserting a new node in a BST MSolution Merge Sort MSolution Number Frequency MSolution Pascal's Triangle MSolution Perfect Square MSolution Powx,n MSolution Quick Sort MSolution Removing Nodes From Linked List MSolution Split BST

▶Backtracking4 · ★1

MBalanced Parentheses MLetter Combinations of a Phone Number MPalindromic Partitioning ★MPermutations II

▶Graphs12 · ★3

MBus Routes ★MClone Graph ★MCourse Schedule MFind Eventual Safe States MFind if Path Exists in Graph MFind the Town Judge MMinimum Number of Vertices to Reach All Nodes MNumber of Provinces MRotting Oranges MShortest Path in a Grid with Obstacles Elimination MWalls and Gates ★MWord Ladder

▶Matrix7 · ★2

MProblem 1 Richest Customer Wealth MProblem 2 Matrix Diagonal Sum MProblem 3 Row With Maximum Ones ★MRotate Image MSet Matrix Zeroes ★MSpiral Matrix MValid Sudoku

▶Dynamic Programming42 · ★14

★MInsert Interval MLongest Substring with At Least K Repeating Characters MMajority Element ★MMerge Intervals MN-th Tribonacci Number MNumber of Dice Rolls With Target Sum MPartition Array for Maximum Sum ★MSolution 01 Knapsack ★MSolution Coin Change MSolution Count of Palindromic Substrings ★MSolution Count of Subset Sum ★MSolution Edit Distance ★MSolution Equal Subset Sum Partition MSolution Fibonacci numbers MSolution House thief MSolution Longest Alternating Subsequence MSolution Longest Bitonic Subsequence ★MSolution Longest Common Subsequence MSolution Longest Common Substring ★MSolution Longest Increasing Subsequence ★MSolution Longest Palindromic Subsequence ★MSolution Longest Palindromic Substring MSolution Longest Repeating Subsequence MSolution Maximum Ribbon Cut MSolution Maximum Sum Increasing Subsequence ★MSolution Minimum Coin Change MSolution Minimum Deletions & Insertions to Transform a String into another MSolution Minimum Deletions in a String to make it a Palindrome MSolution Minimum Deletions to Make a Sequence Sorted MSolution Minimum jumps to reach the end MSolution Minimum jumps with fee ★MSolution Minimum Subset Sum Difference MSolution Number factors MSolution Palindromic Partitioning MSolution Rod Cutting MSolution Shortest Common Super-sequence MSolution Staircase MSolution Strings Interleaving MSolution Subsequence Pattern Matching ★MSolution Subset Sum MSolution Target Sum MSolution Unbounded Knapsack

▶Greedy6 · ★0

MLargest Palindromic Number MMaximum Length of Pair Chain MMinimum Add to Make Parentheses Valid MRemove Duplicate Letters MRemoving Minimum and Maximum From Array MValid Palindrome II

▶Divide & Conquer5 · ★0

MBeautiful Array MLongest Nice Substring MMajority Element MMaximum Binary Tree MSort List

▶Advanced Patterns55 · ★9

MArray Partition MArray Transformation MClone Binary Tree With Random Pointer ★MClone Graph MClone N-ary Tree MClosest Subsequence Sum MContinuous Subarrays MCopy List with Random Pointer MCount Elements With Maximum Frequency MCount Number of Teams MCount of Range Sum MCritical Connections in a Network MDistinct elements in subarray MEncode and Decode Strings MHeight Checker MLeast Number of Unique Integers after K Removals MLongest Continuous Subarray With Absolute Diff Less Than or Equal to Limit MMax Value of Equation MMaximum Gap MMaximum Population Year MMaximum Profitable Triplets With Increasing Prices I MMerge Nodes in Between Zeros MMinimize Malware Spread MMinimize Malware Spread II MMinimum Absolute Difference Queries MMinimum Increment to Make Array Unique MMinimum Number of Coins for Fruits MMinimum Number of Days to Disconnect Island MMinimum Number of Moves to Make Palindrome MMinimum Number of Steps to Make Two Strings Anagram ★MNumber of Longest Increasing Subsequence MPartition Array Into Two Arrays to Minimize Sum Difference MQueries on a Permutation With Key MQueue Reconstruction by Height MRange Frequency Queries MRange Minimum Query MRectangle Area II MRelative Sort Array MRemoving Stars From a String MReverse Pairs ★MSerialize and Deserialize Binary Tree ★MSerialize and Deserialize BST ★MSerialize and Deserialize N-ary Tree MSort Characters By Frequency ★MSpiral Matrix III MSplit Array With Same Average MSubarrays with K Different Integers ★MSubset Sum Equal to Target ★MSubsets having Sum between A and B MSum of Subarray Minimums ★MTop K Frequent Words MValidate Stack Sequences MVerify Preorder Serialization of a Binary Tree MWater Bottles MXOR Queries of a Subarray

▶Company Practice235 · ★56

M'K' Closest Points to the Origin M01 Matrix M132 Pattern M2 Keys Keyboard M4Sum II MAdd Binary ★MAlien Dictionary MArithmetic Slices MArithmetic Slices II - Subsequence MBasic Calculator MBasic Calculator II MBest Meeting Point MBest Time to Buy and Sell MBest Time to Buy and Sell Stock II MBinary Tree Path Sum MBinary Tree Paths MBinary Tree Vertical Order Traversal MBuddy Strings MBuildings With an Ocean View MBuildings With an Ocean View MBurst Balloons MBuy Two Chocolates MCan Place Flowers MCan Place Flowers MCandy MCapacity To Ship Packages Within D Days ★MClone Graph ★MClosest Binary Search Tree Value II ★MCoin Change II ★MCombination Sum ★MCombination Sum MCombinations MConcatenated Words MConstrained Subsequence Sum ★MContainer With Most Water MContiguous Array MCount All Valid Pickup and Delivery Options MCount and Say MCount Array Pairs Divisible by K MCount Nodes Equal to Average of Subtree MCount the Number of Good Subarrays MCount Unique Characters of All Substrings of a Given String MCount Unreachable Pairs of Nodes in an Undirected Graph MCount Vowels Permutation MCustom Sort String ★MDecode Ways MDeepest Leaves Sum MDelete Node in a BST MDesign Add and Search Words Data Structure MDiagonal Traverse MDistribute Coins in Binary Tree MDot Product of Two Sparse Vectors ★MEdit Distance ★MEdit Distance MExcel Sheet Column Title MFair Distribution of Cookies MFind Common Characters MFind Leaves of Binary Tree MFind Leaves of Binary Tree MFind Original Array From Doubled Array MFind Pivot Index MFind the Difference MFind the Difference of Two Arrays MFind the Index of the First Occurrence in a String MFirst Missing Positive MFirst Missing Positive MFizz Buzz MFurthest Building You Can Reach MGray Code ★MHouse Robber II MHow Many Numbers Are Smaller Than the Current Number ★MImplement Trie Prefix Tree MIncreasing Order Search Tree MInorder Successor in BST MIntersection of Two Arrays MIntersection of Two Arrays MIs Subsequence MIsland Perimeter MIsomorphic Strings ★MKth Smallest Number MLargest Odd Number in String MLargest Palindromic Number ★MLargest Rectangle in Histogram ★MLargest Rectangle in Histogram MLargest Submatrix With Rearrangements MLeaf-Similar Trees MLength of Last Word MLength of the Longest Valid Substring MLetter Combinations of a Phone Number MLongest Arithmetic Subsequence MLongest Common Prefix MLongest Increasing Path in a Matrix ★MLongest Increasing Subsequence ★MLongest Palindromic Subsequence ★MLongest Substring Without Repeating Characters ★MLongest Valid Parentheses ★MLowest Common Ancestor of a Binary Search Tree MMake Array Zero by Subtracting Equal Amounts MMake Sum Divisible by P MMaking A Large Island MMatchsticks to Square MMax Consecutive Ones III MMax Points on a Line MMaximize Distance to Closest Person MMaximum Depth or Height of Binary Tree MMaximum Difference Between Node and Ancestor MMaximum Length of a Concatenated String with Unique Characters MMaximum Length of Semi-Decreasing Subarrays MMaximum Length of Subarray With Positive Product MMaximum Level Sum of a Binary Tree MMaximum Number of Balloons MMaximum Points You Can Obtain from Cards ★MMaximum Product Subarray MMaximum Score of a Good Subarray MMaximum Sum of 3 Non-Overlapping Subarrays MMaximum Swap ★MMedian of Two Sorted Arrays ★MMedian of Two Sorted Arrays ★MMeeting Rooms II ★MMerge Intervals ★MMerge Intervals MMerge Strings Alternately MMerge Strings Alternately ★MMerge Two Sorted Lists ★MMin Cost Climbing Stairs MMinimizing Array After Replacing Pairs With Their Product MMinimum Adjacent Swaps to Make a Valid Array MMinimum Area Rectangle MMinimum Deletions to Make Character Frequencies Unique MMinimum Depth of a Binary Tree MMinimum Difference Between Largest and Smallest Value in Three Moves MMinimum Number of Operations to Make Array Empty MMinimum Replacements to Sort the Array MMinimum Suffix Flips MMinimum Time to Type Word Using Special Typewriter ★MMinimum Window Substring MMissing Element in Sorted Array MMissing Ranges MMonotonic Array MMove Zeroes MMoving Average from Data Stream MMultiply Strings MNested List Weight Sum MNext Greater Element II ★MNext Permutation ★MNext Permutation ★MNext Permutation ★MNext Permutation MNth Digit MNth Magical Number MNumber of Flowers in Full Bloom ★MNumber of Islands ★MNumber of Islands ★MNumber of Islands ★MNumber of Islands ★MNumber of Islands MNumber of Provinces MNumber of Substrings Containing All Three Characters MNumber of Valid Subarrays MPair with Target Sum MPalindrome Permutation MPath Crossing MPath with Maximum Sum MPlus One MQuadruple Sum to Target MRank Transform of an Array MRedistribute Characters to Make All Strings Equal MRegular Expression Matching MRelative Sort Array MRemove All Adjacent Duplicates In String MRemove All Ones With Row and Column Flips II MRemove Duplicate Letters MRemove Duplicates from Sorted List ★MRemove Nth Node From End of List MRepeated Substring Pattern MRestore IP Addresses MReverse a LinkedList MReverse a LinkedList MReverse Integer MReverse Integer MReverse Pairs MReverse Words in a String II MRight View of a Binary Tree MRoot Equals Sum of Children ★MRotate Image ★MRotate Image MRotate List MRotting Oranges MSame Tree MScore of Parentheses ★MSearch in Rotated Array MSearch Insert Position MSecond Minimum Node In a Binary Tree ★MSerialize and Deserialize Binary Tree ★MSerialize and Deserialize Binary Tree MSet Mismatch MShortest Path in Binary Matrix MShortest Subarray with Sum at Least K MSimplify Path ★MSingle Number II MSliding Window Maximum MSliding Window Median ★MSolution Coin Change MSolution Take Gifts From the Richest Pile MSpecial Array With X Elements Greater Than or Equal X ★MSpiral Matrix MSplit Linked List in Parts MSqrt MStrobogrammatic Number II ★MSubarray Sum Equals K ★MSubsets MSum of Distances in Tree MSum of Path Numbers MSum of Subarray Minimums MSum of Subarray Minimums MThe kth Factor of n MToeplitz Matrix MTranspose Matrix ★MTrapping Rain Water MTree Diameter ★MTriplet Sum to Zero MUnique Length-3 Palindromic Subsequences MValid Mountain Array MValid Palindrome MValid Palindrome III MValid Parenthesis String MValid Perfect Square MValid Sudoku MValid Sudoku MValid Triangle Number ★MWord Ladder ★MWord Ladder ★MWord Ladder ★MWord Ladder II ★MWord Search