Leetcode笔记

leetcode笔记：Pascal's Triangle II

一.题目描述Givenanindexk,returnthekthrowofthePascal’striangle.Forexample,givenk=3,Return[1,3,3,1].Note:CouldyouoptimizeyouralgorithmtouseonlyO(k)extraspace?二.题目分析关于帕斯卡三角形的定义，可参考：http://baike.baidu.com/link
liyuefeilong·2016-01-11 19:00

leetcode笔记：Pascal's Triangle

一.题目描述GivennumRows,generatethefirstnumRowsofPascal’striangle.Forexample,givennumRows=5,Return:[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ]二.题目分析关于帕斯卡三角形的定义，可参考：http://baike.baidu.com/link?url=qk_-u
liyuefeilong·2016-01-11 01:00

leetcode笔记：Product of Array Except Self

一.题目描述Givenanarrayofnintegerswheren>1,nums,returnanarrayoutputsuchthatoutput[i]isequaltotheproductofalltheelementsofnumsexceptnums[i].SolveitwithoutdivisionandinO(n).Forexample,given[1,2,3,4],return[2
liyuefeilong·2016-01-10 19:00

leetcode笔记：Ugly Number II

一.题目描述Writeaprogramtofindthen-thuglynumber.Uglynumbersarepositivenumberswhoseprimefactorsonlyinclude2,3,5.Forexample,1,2,3,4,5,6,8,9,10,12isthesequenceofthefirst10uglynumbers.Notethat1istypicallytreat
liyuefeilong·2016-01-10 18:00

leetcode笔记：Ugly Number

一.题目描述Writeaprogramtocheckwhetheragivennumberisanuglynumber.Uglynumbersarepositivenumberswhoseprimefactorsonlyinclude2,3,5.Forexample,6,8areuglywhile14isnotuglysinceitincludesanotherprimefactor7.Notet
liyuefeilong·2016-01-10 18:00

leetcode笔记：Power of Three

一.题目描述Givenaninteger,writeafunctiontodetermineifitisapowerofthree.Followup:Couldyoudoitwithoutusinganyloop/recursion?二.题目分析题目的大意很简单，给出一个整数，判断这个整数是不是3的整数次幂。下面提示尽量不适用循环和递归来实现，因此这里给出两种实现方法，其中第一种循环方式的耗时更少
liyuefeilong·2016-01-10 17:00

leetcode笔记

语言：java第二题Youaregiventwolinkedlistsrepresentingtwonon-negativenumbers.Thedigitsarestoredinreverseorderandeachoftheirnodescontainasingledigit.Addthetwonumbersandreturnitasalinkedlist.Input: (2->4->3)+(
landai2011·2016-01-10 15:00

leetcode笔记：Validate Binary Search Tree

一.题目描述Givenabinarytree,determineifitisavalidbinarysearchtree(BST).AssumeaBSTisdefinedasfollows:Theleftsubtreeofanodecontainsonlynodeswithkeyslessthanthenode’skey.Therightsubtreeofanodecontainsonlynode
liyuefeilong·2016-01-07 23:00

leetcode笔记：Leetcode Letter Combinations of a Phone Number

一.题目描述Givenadigitstring,returnallpossiblelettercombinationsthatthenumbercouldrepresent.Amappingofdigittoletters(justlikeonthetelephonebuttons)isgivenbelow.Input:Digitstring"23" Output:["ad","ae","af",
liyuefeilong·2016-01-05 22:00

leetcode笔记：Convert Sorted List to Binary Search Tree

一.题目描述Givenasinglylinkedlistwhereelementsaresortedinascendingorder,convertittoaheightbalancedBST.二.题目分析这道题只要将列表转化为一个数组，就可以使用和题目ConvertSortedArraytoBinarySearchTree一样的方法来进行，这种方法的时间复杂度为O(n)，空间复杂度为O(n^2)
liyuefeilong·2016-01-04 00:00

leetcode笔记：Convert Sorted Array to Binary Search Tree

一.题目描述Givenanarraywhereelementsaresortedinascendingorder,convertittoaheightbalancedBST.二.题目分析将二叉查找树进行中序遍历，就可以得到一个升序排序的数组，因此，一个已经排序的数组可以看做一个中序遍历得到的数组，要得到一个高度平衡的二叉查找树，可以使得左右子树的节点数尽可能相等。因此，可以采用二分法将数组分为两个
liyuefeilong·2016-01-02 21:00

leetcode笔记：Palindrome Number

一.题目描述Determinewhetheranintegerisapalindrome.Dothiswithoutextraspace.Somehints:Couldnegativeintegersbepalindromes?(ie,-1)Ifyouarethinkingofconvertingtheintegertostring,notetherestrictionofusingextrasp
liyuefeilong·2015-12-31 23:00

leetcode笔记：Reverse Integer

一.题目描述Reversedigitsofaninteger.Example1:x=123,return321Example2:x=-123,return-321二.题目分析反转一个整数，若为负数，则负号不变，然后反转负数。该题题设虽然简单，但隐藏一些陷阱，如反转后数字的溢出问题、低位为0时反转到高位时又怎么处理。这种题目目的不是为了考察某种算法，而是考察对各种边界条件是否考虑周全。这里的代码只是
liyuefeilong·2015-12-31 23:00

leetcode笔记：Pow(x, n)

一.题目描述Implementpow(x,n).二.题目分析实现pow(x,n)，即求x的n次幂。最容易想到的方法就是用递归直接求n个x的乘积，这里需要根据n的值，判断结果是正数还是负数，这种方法的时间复杂度为O(n)。更加快捷的方法是，使用分治法，对于x^n，有一下公式：x^n=x^(n/2)*x^(n/2)*x^(n%2)使用这种方法的时间复杂度为O(logn)。三.示例代码#include
liyuefeilong·2015-12-31 23:00

leetcode笔记：Sqrt(x)

一.题目描述Implementintsqrt(intx).Computeandreturnthesquarerootofx.二.题目分析该题要求实现求根公式，该题还算是比较简单的，因为只需返回最接近的整数，直接二分法即可。在实现的过程中还是有一些细节的，比如判断条件：x/mid>mid而不能是x>mid*mid，因为mid*mid会导致溢出。三.示例代码#include usingnamespa
liyuefeilong·2015-12-31 22:00

leetcode笔记：Subsets II

一.题目描述Givenacollectionofintegersthatmightcontainduplicates,nums,returnallpossiblesubsets.Note:Elementsinasubsetmustbeinnon-descendingorder.Thesolutionsetmustnotcontainduplicatesubsets.Forexample,Ifnum
liyuefeilong·2015-12-29 23:00

leetcode笔记：Nim Game

一.题目描述YouareplayingthefollowingNimGamewithyourfriend:Thereisaheapofstonesonthetable,eachtimeoneofyoutaketurnstoremove1to3stones.Theonewhoremovesthelaststonewillbethewinner.Youwilltakethefirstturntorem
liyuefeilong·2015-12-29 00:00

leetcode笔记：Subsets

一.题目描述Givenasetofdistinctintegers,nums,returnallpossiblesubsets.Note:Elementsinasubsetmustbeinnon-descendingorder.Thesolutionsetmustnotcontainduplicatesubsets.Forexample,Ifnums=[1,2,3],asolutionis:[ [
liyuefeilong·2015-12-28 22:00

leetcode笔记：Same Tree

一.题目描述Giventwobinarytrees,writeafunctiontocheckiftheyareequalornot.Twobinarytreesareconsideredequaliftheyarestructurallyidenticalandthenodeshavethesamevalue.二.题目分析题目的意思很简单，判断两棵树是否相同，递归，对两棵树的结点进行比较即可。三
liyuefeilong·2015-12-27 11:00

leetcode笔记：Partition List

一.题目描述Givenalinkedlistandavaluex,partitionitsuchthatallnodeslessthanxcomebeforenodesgreaterthanorequaltox.Youshouldpreservetheoriginalrelativeorderofthenodesineachofthetwopartitions.Forexample,Given1-
liyuefeilong·2015-12-27 01:00

leetcode笔记：Wildcard Matching

一.题目描述Implementwildcardpatternmatchingwithsupportfor‘?’and‘*’.‘?’Matchesanysinglecharacter.‘*’Matchesanysequenceofcharacters(includingtheemptysequence).Thematchingshouldcovertheentireinputstring(notpa
liyuefeilong·2015-12-26 18:00

leetcode笔记：Search Insert Position

一.题目描述Givenasortedarrayandatargetvalue,returntheindexifthetargetisfound.Ifnot,returntheindexwhereitwouldbeifitwereinsertedinorder.Youmayassumenoduplicatesinthearray.Herearefewexamples.[1,3,5,6],5→2 [1
liyuefeilong·2015-12-25 20:00

leetcode笔记：First Bad Version

一.题目描述Youareaproductmanagerandcurrentlyleadingateamtodevelopanewproduct.Unfortunately,thelatestversionofyourproductfailsthequalitycheck.Sinceeachversionisdevelopedbasedonthepreviousversion,alltheversi
liyuefeilong·2015-12-25 17:00

leetcode笔记：Search for a Range

一.题目描述Givenasortedarrayofintegers,findthestartingandendingpositionofagiventargetvalue.Youralgorithm’sruntimecomplexitymustbeintheorderofO(logn).Ifthetargetisnotfoundinthearray,return[-1,-1].Forexample
liyuefeilong·2015-12-25 16:00

leetcode笔记：Sort Colors

一.题目描述Givenanarraywithnobjectscoloredred,whiteorblue,sortthemsothatobjectsofthesamecolorareadjacent,withthecolorsintheorderred,whiteandblue.Here,wewillusetheintegers0,1,and2torepresentthecolorred,whit
liyuefeilong·2015-12-24 23:00

leetcode笔记：First Missing Positive

一.题目描述Givenanunsortedintegerarray,findthefirstmissingpositiveinteger.Forexample,Given[1,2,0]return3,and[3,4,-1,1]return2.YouralgorithmshouldruninO(n)timeandusesconstantspace.二.题目分析该题的大意是给定一个未排序的数组，该数组
liyuefeilong·2015-12-24 01:00

leetcode笔记：Longest Substring Without Repeating Characters

一.题目描述Givenastring,findthelengthofthelongestsubstringwithoutrepeatingcharacters.Forexample,thelongestsubstringwithoutrepeatinglettersfor“abcabcbb”is“abc”,whichthelengthis3.For“bbbbb”thelongestsubstrin
liyuefeilong·2015-12-16 23:00

leetcode笔记：Jump Game II

一.题目描述Givenanarrayofnon-negativeintegers,youareinitiallypositionedatthefirstindexofthearray.Eachelementinthearrayrepresentsyourmaximumjumplengthatthatposition.Yourgoalistoreachthelastindexintheminimum
liyuefeilong·2015-12-16 00:00

leetcode笔记：Jump Game

一.题目描述Givenanarrayofnon-negativeintegers,youareinitiallypositionedatthefirstindexofthearray.Eachelementinthearrayrepresentsyourmaximumjumplengthatthatposition.Determineifyouareabletoreachthelastindex.
liyuefeilong·2015-12-15 23:00

leetcode笔记：Spiral Matrix

一.题目描述Givenamatrixofmnelements(mrows,ncolumns),returnallelementsofthematrixinspiralorder.Forexample,Giventhefollowingmatrix:[ [1,2,3], [4,5,6], [7,8,9] ]Youshouldreturn[1,2,3,6,9,8,7,4,5].二.题目分析题意：给定
liyuefeilong·2015-12-12 21:00

leetcode笔记：Word Ladder

一.题目描述Giventwowords(startandend),andadictionary,findthelengthofshortesttransformationsequencefromstarttoend,suchthat:•Onlyonelettercanbechangedatatime•EachintermediatewordmustexistinthedictionaryForex
liyuefeilong·2015-12-10 23:00

leetcode笔记：Word Search II

一.题目描述Givena2Dboardandalistofwordsfromthedictionary,findallwordsintheboard.Eachwordmustbeconstructedfromlettersofsequentiallyadjacentcell,where“adjacent”cellsarethosehorizontallyorverticallyneighborin
liyuefeilong·2015-12-10 00:00

leetcode笔记：Word Search

一.题目描述Givena2Dboardandaword,findifthewordexistsinthegrid.Thewordcanbeconstructedfromlettersofsequentiallyadjacentcell,where“adjacent”cellsarethosehorizontallyorverticallyneighbouring.Thesamelettercell
liyuefeilong·2015-12-08 23:00

leetcode笔记：Longest Consecutive Sequence

一.题目描述Givenanunsortedarrayofintegers,findthelengthofthelongestconsecutiveelementssequence.Forexample,Given[100,4,200,1,3,2],Thelongestconsecutiveelementssequenceis[1,2,3,4].Returnitslength:4.Youralgor
liyuefeilong·2015-12-03 23:00

leetcode笔记：Construct Binary Tree from Inorder and Postorder Traversal

一.题目描述Giveninorderandpostordertraversalofatree,constructthebinarytree.Note:Youmayassumethatduplicatesdonotexistinthetree.二.题目分析这道题和ConstructBinaryTreefromPreorderandInorderTraversal类似，都是考察基本概念的，后序遍历是先
liyuefeilong·2015-12-01 00:00

leetcode笔记：Construct Binary Tree from Preorder and Inorder Traversal

一.题目描述Givenpreorderandinordertraversalofatree,constructthebinarytree.Note:Youmayassumethatduplicatesdonotexistinthetree.二.题目分析这道题考察了先序和中序遍历，先序是先访问根节点，然后访问左子树，最后访问右子树；中序遍历是先遍历左子树，然后访问根节点，最后访问右子树。做法都是先根
liyuefeilong·2015-11-30 23:00

leetcode笔记：Combination Sum III

一.题目描述Findallpossiblecombinationsofknumbersthatadduptoanumbern,giventhatonlynumbersfrom1to9canbeusedandeachcombinationshouldbeauniquesetofnumbers.Ensurethatnumberswithinthesetaresortedinascendingorder
liyuefeilong·2015-11-27 22:00

leetcode笔记：Combination Sum II

一.题目描述Givenasetofcandidatenumbers(C)andatargetnumber(T),findalluniquecombinationsinCwherethecandidatenumberssumstoT.ThesamerepeatednumbermaybechosenfromConcenumberoftimes.Note:•Allnumbers(includingtar
liyuefeilong·2015-11-27 21:00

leetcode笔记：Combination Sum

一.题目描述Givenasetofcandidatenumbers(C)andatargetnumber(T),findalluniquecombinationsinCwherethecandidatenumberssumstoT.ThesamerepeatednumbermaybechosenfromCunlimitednumberoftimes.Note:•Allnumbers(includi
liyuefeilong·2015-11-25 23:00

leetcode笔记：Restore IP Addresses

一.题目描述Givenastringcontainingonlydigits,restoreitbyreturningallpossiblevalidIPaddresscombinations.Forexample:Given”25525511135”,return[”255.255.11.135”,”255.255.111.35”].(Orderdoesnotmatter)二.题目分析题目的大意
liyuefeilong·2015-11-22 00:00

leetcode笔记：N-Queens II

一.题目描述FollowupforN-Queensproblem.Now,insteadoutputtingboardconfigurations,returnthetotalnumberofdistinctsolutions.二.题目分析题目与N-Queens的方法基本相同，但比后者更为简单，因为题目只要求输出合适解的个数，不需要打印所有解，代码要比上一题简化很多。设一个全局变量，每遍历到底部一
liyuefeilong·2015-11-21 23:00

leetcode笔记：N-Queens

一.题目描述Then-queenspuzzleistheproblemofplacingnqueensonannnchessboardsuchthatnotwoqueensattackeachother.Givenanintegern,returnalldistinctsolutionstothen-queenspuzzle.Eachsolutioncontainsadistinctboardc
liyuefeilong·2015-11-17 23:00

leetcode笔记：Decode Ways

一.题目描述AmessagecontaininglettersfromA-Zisbeingencodedtonumbersusingthefollowingmapping:'A'->1 'B'->2 ... 'Z'->26Givenanencodedmessagecontainingdigits,determinethetotalnumberofwaystodecodeit.Forexample,
liyuefeilong·2015-11-13 23:00

leetcode笔记：Best Time to Buy and Sell Stock IV

一.题目描述Sayyouhaveanarrayforwhichtheithelementisthepriceofagivenstockondayi.Designanalgorithmtofindthemaximumprofit.Youmaycompleteatmostktransactions.Note:Youmaynotengageinmultipletransactionsatthesamet
liyuefeilong·2015-11-12 20:00

leetcode笔记：Best Time to Buy and Sell Stock III

一.题目描述Sayyouhaveanarrayforwhichthei-thelementisthepriceofagivenstockondayi.Designanalgorithmtofindthemaximumprofit.Youmaycompleteatmosttwotransactions.Note:Youmaynotengageinmultipletransactionsatthesa
liyuefeilong·2015-11-12 01:00

leetcode笔记：Best Time to Buy and Sell Stock II

一.题目描述Sayyouhaveanarrayforwhichthei-thelementisthepriceofagivenstockondayi.Designanalgorithmtofindthemaximumprofit.Youmaycompleteasmanytransactionsasyoulike(ie,buyoneandselloneshareofthestockmultiplet
liyuefeilong·2015-11-12 00:00

leetcode笔记：Best Time to Buy and Sell Stock

一.题目描述Sayyouhaveanarrayforwhichthei-thelementisthepriceofagivenstockondayi.Ifyouwereonlypermittedtocompleteatmostonetransaction(ie,buyoneandselloneshareofthestock),designanalgorithmtofindthemaximumpro
liyuefeilong·2015-11-10 23:00

leetcode笔记：Edit Distance

一.题目描述Giventwowordsword1andword2,findtheminimumnumberofstepsrequiredtoconvertword1toword2.(eachoperationiscountedas1step.)Youhavethefollowing3operationspermittedonaword:InsertacharacterDeleteacharacte
liyuefeilong·2015-11-09 16:00

leetcode笔记：Minimum Path Sum

一.题目描述Givenamngridfilledwithnon-negativenumbers,findapathfromtoplefttobottomrightwhichminimizesthesumofallnumbersalongitspath.Note:Youcanonlymoveeitherdownorrightatanypointintime二.题目分析题目的大意是，给定一个m*n的
liyuefeilong·2015-11-08 11:00

leetcode笔记：Interlaving String

一.题目描述Givens1;s2;s3,findwhethers3isformedbytheinterleavingofs1ands2.Forexample,Given:s1=“aabcc”,s2=“dbbca”,Whens3=“aadbbcbcac”,returntrue.Whens3=“aadbbbaccc”,returnfalse.二.题目分析此题可使用二维动态规划来解决，下表给出了直观的匹
liyuefeilong·2015-11-06 13:00
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