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A library of ways to think

Most problems are new; almost none are novel. Four years of contests taught me that behind thousands of problem statements sit a few dozen reusable moves. Sliding windows, disjoint sets, DP over subsets, binary lifting. And learning a move deeply beats skimming a hundred problems shallowly.

This archive is that education, organized: 412 solutions across 19 topics, each kept because the problem was interesting enough to change how I approach the next one. It is also, indirectly, why a 21-hour production job became a 2-second one. Breadth-first search and bitsets were contest moves before they were production moves.

If you're learning: pick one topic, solve until the pattern becomes reflex, then move on. That is the whole method. Search below the way you'd search your own notes.

clone it: git clone https://github.com/Arin016/Data-Structures-and-Algorithms.git

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412 of 412 files

▸STL76

10registration.cpp 11commonabsolutediff.cpp 12multimap.cpp 13priorityqueue.cpp 14candybag.cpp 15reducethearray.cpp 16set.cpp 17studentandgrades.cpp 18setoperations.cpp 19towers.cpp 1vector.cpp 20concatenatearray.cpp 21multiset.cpp 22deque.cpp 23indexedset.cpp 24stlsearching.cpp 25supportqueries.cpp 26validparanthesis.cpp 27countthepairs.cpp 28sortbyrollnumber.cpp 29intersetingame.cpp 2productofdigits.cpp 30meanvarimedianmode.cpp 31Supportqueries2.cpp 32NearestsmallerValues.cpp 33largestrectangle.cpp 34rainwater.cpp 35SuperminimumSum.cpp 36heightofsoilders.cpp 37collissions.cpp 38diversifythearray.cpp 39rebuildoriginalarray.cpp 3Buymaximumobjects.cpp 40roundandround.cpp 41maximumarea.cpp 42gameondeque.cpp 43molecularformula.cpp 44AliceandBooks.cpp 45setqueries.cpp 46AddMul.cpp 47ProductofLastK.cpp 48SnapshotArray.cpp 49sumpair.cpp 4nextpermutation.cpp 50FMBqueue.cpp 51CircularQueue.cpp 52Circulardeque.cpp 53AllOneStringAlgoDesign.cpp 54WordDictionaryTRIE.cpp 55SearchSuggestionsSystemTRIE.cpp 5stack.cpp 6queue.cpp 7queueusing2stack.cpp 8map.cpp 9goodsequence.cpp algodesigMEANMODEVARIANCEMEDIAN.cpp algorithmicdesign.cpp checkbalancedparanthesis.cpp LFUcache.cpp LRUcache.cpp maxofeverywindow.cpp medianusingtopkinsertremoveIdea.cpp minstack.cpp minstackADV.cpp monotonedeque.cpp Multiset2TopKelementssummaintainence.cpp numberofsubarrayswithsumequaltox.cpp paranthesisSTACK.cpp phonepetest.cpp RangeMaintainence1.cpp RangeMaintainence2.cpp saminussbMaximiseyourscoreminimisetheopponentsscore.cpp stackwithincrement.cpp stlapplicationsmaximisenoofitems.cpp TopKelementssummaintainence.cpp windowmaintainance.cpp

▸Dynamic Programming II57

01Knapsack.cpp 0INFknapsack.cpp ADV_MergeElements.cpp Automata_finitestatemachines_Technique.cpp BalancedBracketSequence.cpp BrickColoring.cpp BugsINCode.cpp CherryPickupII.cpp cleaningWindow.cpp climbingstairs.cpp CoinChange.cpp CoinChangeITERATIVE.cpp Coins.cpp CoinsALT.cpp countLIS.cpp CountOfBinarystrings.cpp DECIPHER.cpp DECODINGS.cpp DequeL.cpp destroyColoredGemstones.cpp DIFFutility.cpp DigitDP.cpp DISTINCTsubsequences.cpp Dmagic.cpp DPonGRIDUNIQUE.cpp editDistance.cpp FROGII.cpp GoogleOA_BS.cpp GoogleOA_TREE.cpp HARDsubsequence.cpp isPalindromeQueryDP.cpp JengaTower.cpp KadaneTwist.cpp KnapsackATC.cpp Ksubarrays.cpp LargerString.cpp LCSof2Strings.cpp LCSof3strings.cpp LIS.cpp LISformII.cpp LISnlogn.cpp longestcommonSUBSTRING.cpp MakePalindrome.cpp MakePalindromeALT.cpp MatchSubseq.cpp MatchSubstring.cpp MatrixChainMultiplication.cpp MaximisingTheCOST.cpp maximumAreaofsquare1.cpp MaximumAreaRectangle.cpp MaximumProductSubarray.cpp MaximumScoreGRID.cpp MaximumSUMinSUBGRID.cpp MaximumXOR.cpp MAXSubarraySum.cpp MAXsumPATH2D.cpp MergeElements.cpp

▸Graphs55

01BFS.cpp 1DFS.cpp 1Dijkstra.cpp 2D_Bfs.cpp 2D_Dfs.cpp AllpairsShortestPath.cpp ArticulationPoints.cpp BellmanFord.cpp BFS.cpp BFStopoOrdering.cpp bipartiteCheck.cpp BuildingRoads.cpp burnthemAll.cpp CandyCrush.cpp colorTree.cpp completethegame.cpp connectedCMPsize.cpp DFSGraphGirth.cpp DFSTopoOrdering.cpp DIRECTEDgraphCYCLE.cpp easygraphqueries.cpp EdgeCompression.cpp EdgeReverse.cpp FLOODFILL.cpp FloydWarshall.cpp FMCGSUPPLY.cpp GothamRises.cpp GraphGirth.cpp infectedPeople.cpp KNIGHTS.cpp KwallBreak.cpp minimisingLabels.cpp minimumWalltoBreak.cpp MODELLING.cpp MSSP.cpp MULTIGRAPH.cpp nodeandfuelleft.cpp NOofwaysDIRECTEDgraph.cpp oneEdge.cpp OnePiece.cpp POLICE.cpp Practice_ArticulationPoints.cpp PRIORITYQUEUECUSTOM.cpp roundtrip.cpp roundtrip2.cpp SCC.cpp ShortestDiswithCITYcost.cpp shortestPath1.cpp shortestPath2.cpp SmallestPermutation.cpp SNAKE&Ladders.cpp StringConversionGraphModelling.cpp ThreeStates.cpp topoorderingDP.cpp UNDIRECTEDgraphCYCLE.cpp

▸Dynamic Programming42

▸Trees27

▸Segment Tree19

11BracketQueries.cpp 11EvenOddQueries.cpp 11MergeSortTree.cpp 11MIN.cpp 11MinandCNTmin.cpp 11PrefixSumQueries.cpp 11SubarraySumQueries.cpp 11XOR.cpp basickthSegTree.cpp basickthsegtree1.cpp BasicKthSTD_orderofHeights.cpp basicLAZYdouble.cpp coordinatecompression.cpp DISTINCTinLR.cpp DPAndCoordinateCompression.cpp firsteleGREATEREQUALTOK.cpp NUmofELElessthanorEqualtoKinLR.cpp SalaryQueries.cpp SPL_kthsmallestAi_inLR.cpp

▸Binary search17

2dBSsumvariation.cpp ABC362d.cpp atomicitemcontributions.cpp BSonRealdomain.cpp checkonslopeandeliminatehalves.cpp clasroomlinearcheckfunc.cpp colorBalls.cpp maximisethefraction.cpp maximumsubarrayfilledwithzero.cpp maxlensubarraywithOnewithKflips.cpp medianofsubarray.cpp multiplicationtable.cpp numberandsumofdigit.cpp painterpartition.cpp placingKpointsonnline.cpp sublinear.cpp vectorbyrefvsbyvalue.cpp

▸Recursion and Backtracking15

ABCpuzzle.cpp allsubsequences.cpp androidunlockpattern.cpp atcoder326d.cpp balancedParanthesis.cpp BruteForce.cpp countvalidgridpath.cpp gcd.cpp Kknights.cpp kthpermutation.cpp Nqueens.cpp PrimeCycles.cpp PrimePalindromes.cpp Sudokusolver.cpp temp.cpp

▸two pointers14

3sumtemplate.cpp cntSUBARRAYsumlessthanequaltok.cpp containerwithmaximumwater.cpp countDistcharinsubstrings.cpp countUniquecharinSubstrings.cpp koddnumbers.cpp longestSubarraywithalldistinct.cpp minimumpenalty.cpp optimisedkdistelementsusingarrayanddistcnt.cpp shortestSubarray.cpp templatetwopointers.cpp testing.cpp testing997.cpp threesum.cpp

▸prefix and partial sums13

10TriangleSumQuery.cpp 11HighSchoolMath.cpp 1LRQuery.cpp 2GoodNumbers.cpp 3MultiplySumQuery.cpp 4LRpowerSumQuery.cpp 5APAddition.cpp 6GPaddition.cpp 7KthVal.cpp 8Rectanglesumquery.cpp 9MaxValueinRectangle.cpp CF1108.cpp tempoo.cpp

▸bit manipulation12

1542leetcode.cpp allpairxorsum.cpp and_and_or_relation_with_add.cpp bilkulricksnahileneka.cpp bitbasics.cpp bitsetusage.cpp contributiontechniqueinbits.cpp contributiontechniqueinbitsADV.cpp highesttolowestbitplusprefixsumofbits.cpp maxandsubsequenceklength.cpp submasking.cpp subsetallpaircounting.cpp

▸Disjoint Set Union12

BackToMadras.cpp DSUtemplate.cpp EdgeRemovals.cpp Farthest0fromany1.cpp FULLDSU.cpp GOTHAM_M2.cpp minEdgeWeight.cpp MinimumSpanningTree.cpp MSTRoadReparation.cpp ONEPUNCHMAN.cpp RollbackDSU.cpp weightedDSU.cpp

▸number theory12

eulersphifunction.cpp fastfactorisation.cpp largestpowerofxinnfactorial.cpp nbyipowern.cpp onebyxplusonebyy.cpp onebyxplusonebyyADVV.cpp pairedcubes.cpp segmentedsieve.cpp sieve.cpp sumoffirstntermsmodulom.cpp test170724.cpp totient.cpp

▸Tries12

ADV_XOR_designastructure.cpp AutoSuggestions.cpp BITtrie.cpp goodsubstringsM1.cpp goodsubstringsM2.cpp INCREMENTALbuilding.cpp Max_XOR_subarray.cpp mismatchQueries.cpp trie1.cpp trie2.cpp trie3.cpp XOR_designastructure.cpp

▸String algorithms11

KMPalgorithm.cpp LEXIsmallest_cyclicShifts.cpp longestcommonsubstring.cpp longestPalindromeSubstring.cpp ManacherAlgorithm.cpp periodofastring.cpp prefixSuffixMiddle.cpp rollinghash.cpp SuffixArray.cpp XORney.cpp Zalgorithm.cpp

▸sweep line9

amazonsweepline.cpp DEshaw1stques.cpp intersectionandunion.cpp nsegqueriesofy.cpp solveintervals1.cpp solveintervals2.cpp solveintervals3.cpp sweepandtopkqueries.cpp sweepline.cpp

▸meet in the middle6

betterVersion_squarePartition.cpp fourNumberSum.cpp ModuloSubsequences.cpp squarePartition.cpp StringReversals.cpp subsetSum.cpp

▸Divide and conquer2

mergesort.cpp templatemergesort.cpp

▸Modular Arithmetic1