Leetcode题解

LeetCode题解：Sort Colors

SortColorsGivenanarraywithnobjectscoloredred,whiteorblue,sortthemsothatobjectsofthesamecolorareadjacent,withthecolorsintheorderred,whiteandblue.Here,wewillusetheintegers0,1,and2torepresentthecolorred,
MagiSu·2013-11-13 12:00

LeetCode题解：N-Queens I and II

N-QueensThen-queenspuzzleistheproblemofplacingnqueensonann×nchessboardsuchthatnotwoqueensattackeachother.Givenanintegern,returnalldistinctsolutionstothen-queenspuzzle.Eachsolutioncontainsadistinctboar
MagiSu·2013-11-13 11:00

LeetCode题解：Palindrome Number

PalindromeNumberDeterminewhetheranintegerisapalindrome.Dothiswithoutextraspace.思路：题目要求只能用O(1)的空间，所以不能考虑把它转化为字符串然后reverse比较的方法。在提示中也提到了，如果考虑reversenumber的方法，可能造成溢出。那么只能选择分离数字的方法，当然要用到大量除10和取余数的计算。真是一件悲
MagiSu·2013-11-13 11:00

LeetCode题解：Remove Nth Node from End of List

RemoveNthNodeFromEndofListGivenalinkedlist,removethenthnodefromtheendoflistandreturnitshead.Forexample,Givenlinkedlist:1->2->3->4->5,andn=2. Afterremovingthesecondnodefromtheend,thelinkedlistbecomes1
MagiSu·2013-11-10 10:00

LeetCode题解：Minimum Path Sum

MinimumPathSumGivenamxngridfilledwithnon-negativenumbers,findapathfromtoplefttobottomrightwhichminimizesthesumofallnumbersalongitspath.Note:Youcanonlymoveeitherdownorrightatanypointintime.思路：一个简单的动态规划
MagiSu·2013-11-10 06:00

LeetCode题解：Gray Code

GrayCodeThegraycodeisabinarynumeralsystemwheretwosuccessivevaluesdifferinonlyonebit.Givenanon-negativeintegernrepresentingthetotalnumberofbitsinthecode,printthesequenceofgraycode.Agraycodesequencemust
MagiSu·2013-11-10 05:00

LeetCode题解：Convert Sorted Array to Binary Search Tree

ConvertSortedArraytoBinarySearchTreeGivenanarraywhereelementsaresortedinascendingorder,convertittoaheightbalancedBST.思路：给定一个区间[left,right]，取其中值mid=(left+right)/2对应的元素作为二叉树的根。二叉树的左子树根的值为对[left,mid-1]继续
MagiSu·2013-11-10 05:00

【LeetCode题解】Remove Element

RemoveElement （Java代码）MySubmissionsGivenanarrayandavalue,removeallinstancesofthatvalueinplaceandreturnthenewlength.Theorderofelementscanbechanged.Itdoesn'tmatterwhatyouleavebeyondthenewlength.publiccl
cc1044588189·2013-11-09 22:00

【LeetCode题解】Search Insert Position

SearchInsertPosition （Java代码）Givenasortedarrayandatargetvalue,returntheindexifthetargetisfound.Ifnot,returntheindexwhereitwouldbeifitwereinsertedinorder.Youmayassumenoduplicatesinthearray.Herearefewex
cc1044588189·2013-11-09 21:00

【LeetCode题解】Single Number II

SingleNumberII （Java代码）Givenanarrayofintegers,everyelementappears three timesexceptforone.Findthatsingleone.Note:Youralgorithmshouldhavealinearruntimecomplexity.Couldyouimplementitwithoutusingextramem
cc1044588189·2013-11-08 17:00

LeetCode题解：Partition List

PartitionListGivenalinkedlistandavaluex,partitionitsuchthatallnodeslessthanxcomebeforenodesgreaterthanorequaltox.Youshouldpreservetheoriginalrelativeorderofthenodesineachofthetwopartitions.Forexample,
MagiSu·2013-11-07 04:00

【LeetCode题解】Reverse Integer

ReverseInteger（Java代码）Reversedigitsofaninteger.Example1: x=123,return321Example2: x=-123,return-321clicktoshowspoilers.Haveyouthoughtaboutthis?Herearesomegoodquestionstoaskbeforecoding.Bonuspointsfory
cc1044588189·2013-11-06 00:00

【LeetCode题解】Single Number

SingleNumber（Java代码）Givenanarrayofintegers,everyelementappears twice exceptforone.Findthatsingleone.Note:Youralgorithmshouldhavealinearruntimecomplexity.Couldyouimplementitwithoutusingextramemory?解题思路
cc1044588189·2013-11-06 00:00

LeetCode题解：Symmetric Tree

SymmetricTreeGivenabinarytree,checkwhetheritisamirrorofitself(ie,symmetricarounditscenter).Forexample,thisbinarytreeissymmetric:1 /\ 22 /\/\ 3443 Butthefollowingisnot:1 /\ 22 \\ 33 Note:Bonuspointsify
MagiSu·2013-11-05 16:00

LeetCode题解：Climbing Stairs

ClimbingStairsYouareclimbingastaircase.Ittakesnstepstoreachtothetop.Eachtimeyoucaneitherclimb1or2steps.Inhowmanydistinctwayscanyouclimbtothetop?思路：这种题目属于那种“想到解法就很快做出”的类型。n个台阶的楼梯的走法等于：ways(n)=ways(n-1)
MagiSu·2013-11-05 15:00

LeetCode题解：Search Insert Position

SearchInsertPositionGivenasortedarrayandatargetvalue,returntheindexifthetargetisfound.Ifnot,returntheindexwhereitwouldbeifitwereinsertedinorder.Youmayassumenoduplicatesinthearray.Herearefewexamples.[1
MagiSu·2013-11-05 15:00

LeetCode题解：Populating Next Right Pointers in Each Node I and II

PopulatingNextRightPointersinEachNodeGivenabinarytreestructTreeLinkNode{ TreeLinkNode*left; TreeLinkNode*right; TreeLinkNode*next; } Populateeachnextpointertopointtoitsnextrightnode.Ifthereisnonextrig
MagiSu·2013-11-05 15:00

LeetCode题解：Remove Element

RemoveElementGivenanarrayandavalue,removeallinstancesofthatvalueinplaceandreturnthenewlength.Theorderofelementscanbechanged.Itdoesn'tmatterwhatyouleavebeyondthenewlength.思路：左右两个指针依次指向数组开始和结束。左右指针移动，将所
MagiSu·2013-11-05 14:00

LeetCode题解：Same Tree

SameTreeGiventwobinarytrees,writeafunctiontocheckiftheyareequalornot.Twobinarytreesareconsideredequaliftheyarestructurallyidenticalandthenodeshavethesamevalue.思路：递归比较即可。题解：/** *Definitionforbinarytree
MagiSu·2013-11-05 10:00

LeetCode题解：Linked List Cycle

LinkedListCycleGivenalinkedlist,determineifithasacycleinit.Followup:Canyousolveitwithoutusingextraspace?思路：参见ElementsofProgramming，其中讨论orbit的时候提到了这个问题的方法。也就是选择两个指针，一个指针跑得比另外一个指针快。如果跑得快的指针遇到了终点，那么就不存在环
MagiSu·2013-11-05 09:00

LeetCode题解：Integer to Roman

IntegertoRomanGivenaninteger,convertittoaromannumeral.Inputisguaranteedtobewithintherangefrom1to3999.思路：没有思路。题解：classSolution{ public: stringintToRoman(intnum){ staticconststringSYMBOLS="MDCLXVI"; st
MagiSu·2013-11-05 09:00

LeetCode题解：Reorder List

ReorderListGivenasinglylinkedlistL:L0→L1→…→Ln-1→Ln,reorderitto:L0→Ln→L1→Ln-1→L2→Ln-2→…Youmustdothisin-placewithoutalteringthenodes'values.Forexample,Given{1,2,3,4},reorderitto{1,4,2,3}.思路：因为链表是单向的，只能通
MagiSu·2013-11-05 09:00

LeetCode题解：Multiply Strings

MultiplyStringsGiventwonumbersrepresentedasstrings,returnmultiplicationofthenumbersasastring.Note:Thenumberscanbearbitrarilylargeandarenon-negative.思路：两件事情：1.字符串表示的数字和单个字符表示的数字的乘法2.两个字符串表示的数字的求和。这些都是初
MagiSu·2013-11-05 09:00

LeetCode题解：Remove Duplicates from Sorted Array I and II

RemoveDuplicatesfromSortedArrayIIFollowupfor"RemoveDuplicates":Whatifduplicatesareallowedatmosttwice?Forexample,GivensortedarrayA=[1,1,1,2,2,3],Yourfunctionshouldreturnlength=5,andAisnow[1,1,2,2,3].Re
MagiSu·2013-11-05 06:00

LeetCode题解：Clone Graph

CloneGraphCloneanundirectedgraph.Eachnodeinthegraphcontainsalabelandalistofitsneighbors.思路：首先对这个图进行搜索，深度优先广度优先是任意的。每碰到一个之前未遇到的结点则创造一个相应的新结点与这个结点对照，同时新结点的所有邻居仍然和原始结点的邻居相同。然后更新新结点的邻居信息，在之前的搜索中新旧结点的对应关系是
MagiSu·2013-11-05 05:00

LeetCode题解：Spiral Matrix I and II

SpiralMatrixGivenamatrixofmxnelements(mrows,ncolumns),returnallelementsofthematrixinspiralorder.Forexample,Giventhefollowingmatrix:[ [1,2,3], [4,5,6], [7,8,9] ] Youshouldreturn[1,2,3,6,9,8,7,4,5].Spir
MagiSu·2013-11-05 04:00

LeetCode题解：Search a 2D Matrix

Searcha2DMatrixWriteanefficientalgorithmthatsearchesforavalueinanmxnmatrix.Thismatrixhasthefollowingproperties:Integersineachrowaresortedfromlefttoright.Thefirstintegerofeachrowisgreaterthanthelastint
MagiSu·2013-11-05 04:00

LeetCode题解：Rotate Image

RotateImageYouaregivenannxn2Dmatrixrepresentinganimage.Rotatetheimageby90degrees(clockwise).Followup:Couldyoudothisin-place?思路：可以参见ProgrammingPearls，很多时候旋转是可以用reverse代替的。做顺时针90度旋转，可以先转置矩阵，然后对矩阵的每一行进行r
MagiSu·2013-11-05 03:00

LeetCode题解：Triangle

TriangleGivenatriangle,findtheminimumpathsumfromtoptobottom.Eachstepyoumaymovetoadjacentnumbersontherowbelow.Forexample,giventhefollowingtriangle[ [2], [3,4], [6,5,7], [4,1,8,3] ] Theminimumpathsumfro
MagiSu·2013-11-05 01:00

LeetCode题解：Minimum Depth of Binary Tree

MinimumDepthofBinaryTreeGivenabinarytree,finditsminimumdepth.Theminimumdepthisthenumberofnodesalongtheshortestpathfromtherootnodedowntothenearestleafnode.思路：首先要区分两种结点：非leaf的结点和leaf的结点。leaf结点的左右子树均为空。然
MagiSu·2013-11-05 01:00

LeetCode题解：Binary Tree Level Order Traversal I and II

BinaryTreeLevelOrderTraversalGivenabinarytree,returnthelevelordertraversalofitsnodes'values.(ie,fromlefttoright,levelbylevel).Forexample:Givenbinarytree{3,9,20,#,#,15,7},3 /\ 920 /\ 157 returnitslevel
MagiSu·2013-11-04 11:00

LeetCode题解：Permutations I and II

PermutationsGivenacollectionofnumbers,returnallpossiblepermutations.Forexample,[1,2,3]havethefollowingpermutations:[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],and[3,2,1].PermutationsIIGivenacollectionofnu
MagiSu·2013-11-04 02:00

LeetCode题解：Interleaving String

InterleavingStringGivens1,s2,s3,findwhethers3isformedbytheinterleavingofs1ands2.Forexample,Given:s1="aabcc",s2="dbbca",Whens3="aadbbcbcac",returntrue.Whens3="aadbbbaccc",returnfalse.思路：其实是一个动态规划问题：设o1
MagiSu·2013-11-04 02:00

LeetCode题解：Next Permutation

NextPermutationImplementnextpermutation,whichrearrangesnumbersintothelexicographicallynextgreaterpermutationofnumbers.Ifsucharrangementisnotpossible,itmustrearrangeitasthelowestpossibleorder(ie,sorted
MagiSu·2013-11-04 00:00

LeetCode题解：Minimum Window Substring

MinimumWindowSubstringGivenastringSandastringT,findtheminimumwindowinSwhichwillcontainallthecharactersinTincomplexityO(n).Forexample,S="ADOBECODEBANC"T="ABC"Minimumwindowis"BANC".Note:Ifthereisnosuchw
MagiSu·2013-11-03 23:00

LeetCode题解：Roman to Integer

RomantoIntegerGivenaromannumeral,convertittoaninteger.Inputisguaranteedtobewithintherangefrom1to3999.思路：字母对数字的一一对应累积关系。唯一需要注意的是，之前一个字母对应的数字如果小于当前字母对应的数字，则需要特殊处理。题解：std::mapchar_mapper{ {'I',1}, {'V',5
MagiSu·2013-11-02 06:00

LeetCode题解：Simplify Path

SimplifyPathGivenanabsolutepathforafile(Unix-style),simplifyit.Forexample,path="/home/",=>"/home"path="/a/./b/../../c/",=>"/c"思路：其实就是一个依次处理以'/'为分割的数据的工具。如果碰到空输入或者'.'就什么都不做，如果碰到".."就从队列里退出一个元素。最后将队列里的元
MagiSu·2013-11-02 06:00

LeetCode题解：Remove Duplicates from Sorted List II

RemoveDuplicatesfromSortedListIIGivenasortedlinkedlist,deleteallnodesthathaveduplicatenumbers,leavingonlydistinctnumbersfromtheoriginallist.Forexample,Given1->2->3->3->4->4->5,return1->2->5.Given1->1-
MagiSu·2013-11-02 05:00

LeetCode题解：Remove Duplicates from Sorted List

RemoveDuplicatesfromSortedListGivenasortedlinkedlist,deleteallduplicatessuchthateachelementappearonlyonce.Forexample,Given1->1->2,return1->2.Given1->1->2->3->3,return1->2->3.思路：用两个指针。一个指针不断前进，另一个指针不动。
MagiSu·2013-11-02 02:00

LeetCode题解：Letter Combinations of a Phone Number

LetterCombinationsofaPhoneNumberGivenadigitstring,returnallpossiblelettercombinationsthatthenumbercouldrepresent.Amappingofdigittoletters(justlikeonthetelephonebuttons)isgivenbelow.Input:Digitstring"2
MagiSu·2013-10-31 03:00

LeetCode题解：Pascal's triangle I and II

Pascal'sTriangleGivennumRows,generatethefirstnumRowsofPascal'striangle.Forexample,givennumRows=5,Return[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ]Pascal'sTriangleIIGivenanindexk,returnthekthrowoft
MagiSu·2013-10-31 03:00

LeetCode题解：Reverse integer

ReverseIntegerReversedigitsofaninteger.Example1:x=123,return321Example2:x=-123,return-321思路：不断用对10取余的方法分离数字，然后反过来即可。注意符号位。题解：classSolution{ public: intreverse(intx){ intflag=(x>=0?1:-1); x*=flag; intr
MagiSu·2013-10-27 13:00

LeetCode题解：Single Number I and II

SingleNumberGivenanarrayofintegers,everyelementappearstwiceexceptforone.Findthatsingleone.Note:Youralgorithmshouldhavealinearruntimecomplexity.Couldyouimplementitwithoutusingextramemory?SingleNumberII
MagiSu·2013-10-27 13:00

LeetCode题解：Maximum Depth of Binary Tree

MaximumDepthofBinaryTreeGivenabinarytree,finditsmaximumdepth.Themaximumdepthisthenumberofnodesalongthelongestpathfromtherootnodedowntothefarthestleafnode.思路：树其实是图的一种特例。在对树进行搜索的时候保留树深的信息。一旦遇到深度比已知最大深度大
MagiSu·2013-10-27 13:00

LeetCode题解：Copy List with Random Pointer

CopyListwithRandomPointerAlinkedlistisgivensuchthateachnodecontainsanadditionalrandompointerwhichcouldpointtoanynodeinthelistornull.Returnadeepcopyofthelist.思路：比起标准的链表深拷贝，还需要了解一个randompointer的信息。需要建立起
MagiSu·2013-10-27 13:00

LeetCode题解：Valid Palindrome

ValidPalindromeGivenastring,determineifitisapalindrome,consideringonlyalphanumericcharactersandignoringcases.Forexample,"Aman,aplan,acanal:Panama"isapalindrome."raceacar"isnotapalindrome.Note:Haveyouc
MagiSu·2013-10-27 08:00

LeetCode题解：Restore IP Addresses

RestoreIPAddressesGivenastringcontainingonlydigits,restoreitbyreturningallpossiblevalidIPaddresscombinations.Forexample:Given"25525511135",return["255.255.11.135","255.255.111.35"].(Orderdoesnotmatter
MagiSu·2013-10-27 04:00

LeetCode题解：Unique Paths II

UniquePathsIIFollowupfor"UniquePaths":Nowconsiderifsomeobstaclesareaddedtothegrids.Howmanyuniquepathswouldtherebe?Anobstacleandemptyspaceismarkedas1and0respectivelyinthegrid.Forexample,Thereisoneobsta
MagiSu·2013-10-26 19:00

LeetCode题解：Unique Paths

UniquePathsArobotislocatedatthetop-leftcornerofamxngrid(marked'Start'inthediagrambelow).Therobotcanonlymoveeitherdownorrightatanypointintime.Therobotistryingtoreachthebottom-rightcornerofthegrid(marke
MagiSu·2013-10-26 19:00

LeetCode题解：Valid Sudoku

ValidSudokuDetermineifaSudokuisvalid,accordingto:SudokuPuzzles-TheRules.TheSudokuboardcouldbepartiallyfilled,whereemptycellsarefilledwiththecharacter'.'.Apartiallyfilledsudokuwhichisvalid.思路：遍历整个棋盘，记录
MagiSu·2013-10-26 15:00
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