Leetcode题解

LeetCode题解：Binary Tree Inorder Traversal

Givenabinarytree,returntheinordertraversalofitsnodes’values.Forexample:Givenbinarytree{1,#,2,3},1\2/3return[1,3,2].题意：中序遍历二叉树解决思路：”左根右“的递归或者通过栈完成的迭代代码：publicclassSolution{ publicListinorderTraversal(T
u012403246·2015-10-02 19:00

LeetCode题解：Restore IP Addresses

Givenastringcontainingonlydigits,restoreitbyreturningallpossiblevalidIPaddresscombinations.Forexample:Given“25525511135”,return[“255.255.11.135”,“255.255.111.35”].(Orderdoesnotmatter)题意：给定一个字符串，判断其代表的
u012403246·2015-10-02 19:00

LeetCode题解：Reverse Linked List II

Reversealinkedlistfrompositionmton.Doitin-placeandinone-pass.Forexample:Given1->2->3->4->5->NULL,m=2andn=4,return1->4->3->2->5->NULL.Note:Givenm,nsatisfythefollowingcondition:1≤m≤n≤lengthoflist.题意：给定整
u012403246·2015-10-02 19:00

LeetCode题解：Decode Ways

AmessagecontaininglettersfromA-Zisbeingencodedtonumbersusingthefollowingmapping:‘A’->1‘B’->2…‘Z’->26Givenanencodedmessagecontainingdigits,determinethetotalnumberofwaystodecodeit.Forexample,Givenencode
u012403246·2015-10-02 19:00

LeetCode题解——Convert Sorted Array to Binary Search Tree

Givenanarraywhereelementsaresortedinascendingorder,convertittoaheightbalancedBST./** *Definitionforabinarytreenode. *structTreeNode{ *intval; *TreeNode*left; *TreeNode*right; *TreeNode(intx):val(x),le
u010025211·2015-09-30 16:00

LeetCode题解——Convert Sorted List to Binary Search Tree

Givenasinglylinkedlistwhereelementsaresortedinascendingorder,convertittoaheightbalancedBST.分析:要求最后得到一颗平衡二叉树，那么链表的中间节点就是二叉树的根节点，中间节点左边就是二叉树的左子树，中间节点右边就是二叉树的右子树首先找到链表的中间节点作为BST的根节点，根节点的左子树是以中间节点左边的节点建立的
u010025211·2015-09-30 16:00

LeetCode题解——Implement Queue using Stacks

Implementthefollowingoperationsofaqueueusingstacks.push(x)--Pushelementxtothebackofqueue.pop()--Removestheelementfrominfrontofqueue.peek()--Getthefrontelement.empty()--Returnwhetherthequeueisempty.Not
u010025211·2015-09-29 15:00

LeetCode题解——Implement Stack using Queues

Implementthefollowingoperationsofastackusingqueues.push(x)--Pushelementxontostack.pop()--Removestheelementontopofthestack.top()--Getthetopelement.empty()--Returnwhetherthestackisempty.Notes:Youmustuse
u010025211·2015-09-29 15:00

LeetCode题解——Add Digits

Givenanon-negativeinteger num,repeatedlyaddallitsdigitsuntiltheresulthasonlyonedigit.Forexample:Given num=38,theprocessislike: 3+8=11, 1+1=2.Since 2 hasonlyonedigit,returnit.Followup:Couldyoudoitwitho
u010025211·2015-09-29 11:00

LeetCode题解——Linked List Cycle II

explannationfrom:http://stackoverflow.com/questions/2936213/explain-how-finding-cycle-start-node-in-cycle-linked-list-workLetmetrytoclarifythecycledetectionalgorithmthatisprovidedathttp://en.wikipedia
u010025211·2015-09-25 11:00

LeetCode题解——Linked List Cycle

Givenalinkedlist,determineifithasacycleinit.Followup:Canyousolveitwithoutusingextraspace?/** *Definitionforsingly-linkedlist. *structListNode{ *intval; *ListNode*next; *ListNode(intx):val(x),next(NULL
u010025211·2015-09-25 10:00

LeetCode题解——Intersection of Two Linked Lists

Writeaprogramtofindthenodeatwhichtheintersectionoftwosinglylinkedlistsbegins.Forexample,thefollowingtwolinkedlists:A:a1→a2 ↘ c1→c2→c3 ↗ B:b1→b2→b3 begintointersectatnodec1.Notes:Ifthetwolinkedlistshav
u010025211·2015-09-25 09:00

LeetCode题解——Rotate Array

Rotateanarrayof n elementstotherightby k steps.Forexample,with n =7and k =3,thearray [1,2,3,4,5,6,7] isrotatedto [5,6,7,1,2,3,4].Note:Trytocomeupasmanysolutionsasyoucan,thereareatleast3differentwaysto
u010025211·2015-09-23 14:00

LeetCode题解：Subsets II

Givenacollectionofintegersthatmightcontainduplicates,nums,returnallpossiblesubsets.Note:Elementsinasubsetmustbeinnon-descendingorder.Thesolutionsetmustnotcontainduplicatesubsets.Forexample,Ifnums=[1,2
u012403246·2015-09-06 21:00

LeetCode题解：Subsets

Givenasetofdistinctintegers,nums,returnallpossiblesubsets.Note:Elementsinasubsetmustbeinnon-descendingorder.Thesolutionsetmustnotcontainduplicatesubsets.Forexample,Ifnums=[1,2,3],asolutionis:[[3],[1],
u012403246·2015-09-06 21:00

LeetCode题解：Search Insert Position

Givenasortedarrayandatargetvalue,returntheindexifthetargetisfound.Ifnot,returntheindexwhereitwouldbeifitwereinsertedinorder.Youmayassumenoduplicatesinthearray.Herearefewexamples.[1,3,5,6],5→2[1,3,5,6]
u012403246·2015-09-06 21:00

LeetCode题解：Group Anagrams

Givenanarrayofstrings,groupanagramstogether.Forexample,given:[“eat”,“tea”,“tan”,“ate”,“nat”,“bat”],Return:[[“ate”,“eat”,”tea”],[“nat”,”tan”],[“bat”]]Note:Forthereturnvalue,eachinnerlist’selementsmustf
u012403246·2015-09-06 21:00

LeetCode题解：Permutations

Givenacollectionofnumbers,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].题意：求出给定数字的所有组合可能解决思路：先加入第一个元素，然后把第二个元素插入两个位置中，
u012403246·2015-09-06 21:00

LeetCode题解：Search for a Range

Givenasortedarrayofintegers,findthestartingandendingpositionofagiventargetvalue.Youralgorithm’sruntimecomplexitymustbeintheorderofO(logn).Ifthetargetisnotfoundinthearray,return[-1,-1].Forexample,Given
u012403246·2015-09-06 21:00

LeetCode题解：Next Permutation

Implementnextpermutation,whichrearrangesnumbersintothelexicographicallynextgreaterpermutationofnumbers.Ifsucharrangementisnotpossible,itmustrearrangeitasthelowestpossibleorder(ie,sortedinascendingorde
u012403246·2015-09-06 21:00

LeetCode题解：Divide Two Integers

Dividetwointegerswithoutusingmultiplication,divisionandmodoperator.Ifitisoverflow,returnMAX_INT.题意：不使用乘，除，模符号作除法运算解决思路：每一个数都可以用2进制表示，利用这一点通过位运算完成代码：publicclassSolution{ publicintdivide(intdividend,int
u012403246·2015-09-06 20:00

LeetCode题解：Swap Nodes in Pairs

Givenalinkedlist,swapeverytwoadjacentnodesandreturnitshead.Forexample,Given1->2->3->4,youshouldreturnthelistas2->1->4->3.Youralgorithmshoulduseonlyconstantspace.Youmaynotmodifythevaluesinthelist,onlyn
u012403246·2015-09-06 20:00

LeetCode题解：Construct Binary Tree from Preorder and Inorder Traversal

Givenpreorderandinordertraversalofatree,constructthebinarytree.Note:Youmayassumethatduplicatesdonotexistinthetree.题意：给定一棵树的先序遍历和中序遍历，还原该树解决思路：在中序遍历中，每一个根节点的左方为其左子树，右方为右子树；而在先序遍历中第一个节点为根节点。利用这两点可以解决代码：
u012403246·2015-09-06 20:00

leetcode题解

/** *Definitionforsingly-linkedlist. *structListNode{ *intval; *ListNode*next; *ListNode(intx):val(x),next(NULL){} *}; */ classSolution{ public: boolisPalindrome(ListNode*head){ if(head==NULL||head->n
xtzmm1215·2015-08-27 21:00

LeetCode题解：Add Digits

Givenanon-negativeintegernum,repeatedlyaddallitsdigitsuntiltheresulthasonlyonedigit.Forexample:Givennum=38,theprocessislike:3+8=11,1+1=2.Since2hasonlyonedigit,returnit.题意：给定非负整数，不断把各位数字相加，直到结果是个位数。例如3
u012403246·2015-08-21 09:00

LeetCode题解：Binary Tree Paths

Givenabinarytree,returnallroot-to-leafpaths.Forexample,giventhefollowingbinarytree:1/\23\5Allroot-to-leafpathsare:["1->2->5","1->3"]题意：给定一颗二叉树，返回所有从根节点到叶节点的路径解决思路：DFS代码：publicclassSolution{ publicList
u012403246·2015-08-21 09:00

LeetCode题解：Roman to Integer

Givenaromannumeral,convertittoaninteger.Inputisguaranteedtobewithintherangefrom1to3999.题意：给定一个1-3999范围内的罗马数字，把它转换为整数解决思路：按照罗马数字转换代码：publicclassSolution{ publicintromanToInt(Strings){ intres=0; for(int
u012403246·2015-08-21 09:00

LeetCode题解：Longest Common Prefix

Writeafunctiontofindthelongestcommonprefixstringamongstanarrayofstrings.题意：找出字符串数组中最长的共有前缀解决思路：遍历所有字符串从头到尾找共有前缀代码：publicclassSolution{ publicStringlongestCommonPrefix(String[]strs){ if(strs.length==0)
u012403246·2015-08-21 09:00

LeetCode题解：Remove Nth Node From End of List

Givenalinkedlist,removethenthnodefromtheendoflistandreturnitshead.Forexample,Givenlinkedlist:1->2->3->4->5,andn=2.Afterremovingthesecondnodefromtheend,thelinkedlistbecomes1->2->3->5.Note:Givennwillalw
u012403246·2015-08-21 09:00

LeetCode题解：Contains Duplicate II

Givenanarrayofintegersandanintegerk,findoutwhethertherearetwodistinctindicesiandjinthearraysuchthatnums[i]=nums[j]andthedifferencebetweeniandjisatmostk.题意：给定数组和整数k，找出数组内相同元素，且两个元素距离小于等于k解决思路：和前一个思路一样，
u012403246·2015-08-12 11:00

LeetCode题解：Contains Duplicate

Givenanarrayofintegers,findifthearraycontainsanyduplicates.Yourfunctionshouldreturntrueifanyvalueappearsatleasttwiceinthearray,anditshouldreturnfalseifeveryelementisdistinct.题意：给定一个整数数组，判断是否含有重复元素解决思路
u012403246·2015-08-12 11:00

LeetCode题解：Rectangle Area

Findthetotalareacoveredbytworectilinearrectanglesina2Dplane.Eachrectangleisdefinedbyitsbottomleftcornerandtoprightcornerasshowninthefigure.Assumethatthetotalareaisneverbeyondthemaximumpossiblevalueofi
u012403246·2015-08-12 11:00

LeetCode题解：Implement Stack using Queues

Implementthefollowingoperationsofastackusingqueues.push(x)–Pushelementxontostack.pop()–Removestheelementontopofthestack.top()–Getthetopelement.empty()–Returnwhetherthestackisempty.Notes:Youmustuseonly
u012403246·2015-08-12 11:00

LeetCode题解：Invert Binary Tree

Invertabinarytree.4/\27/\/\1369to4/\72/\/\9631题意：将二叉树的左右子树互换解决思路：DFS或BFS代码：DFS：publicTreeNodeinvertTree(TreeNoderoot){ if(root==null){ returnnull; } finalTreeNodeleft=root.left, right=root.right; roo
u012403246·2015-08-12 10:00

LeetCode题解：Summary Ranges

Givenasortedintegerarraywithoutduplicates,returnthesummaryofitsranges.Forexample,given[0,1,2,4,5,7],return[“0->2”,”4->5”,”7”].题意：给定一个有序数组，数组内没有重复元素，返回一个代表数组内数据范围的数组。解决思路：从左往右遍历，当后一个元素与当前元素差不为1的时候就输出数据
u012403246·2015-08-12 10:00

LeetCode题解：Power of Two

Givenaninteger,writeafunctiontodetermineifitisapoweroftwo.题意：给定一个整数，判断是否为2的幂解决思路：如果一个整数n是2的幂，那么让n和n-1进行与运算必然为0（位运算）代码：publicbooleanisPowerOfTwo(intn){ return((n&(n-1))==0&&n>0); }
u012403246·2015-08-12 10:00

LeetCode题解：Implement Queue using Stacks

Implementthefollowingoperationsofaqueueusingstacks.push(x)–Pushelementxtothebackofqueue.pop()–Removestheelementfrominfrontofqueue.peek()–Getthefrontelement.empty()–Returnwhetherthequeueisempty.Notes:Y
u012403246·2015-08-12 10:00

LeetCode题解：Palindrome Linked List

Givenasinglylinkedlist,determineifitisapalindrome.Followup:CouldyoudoitinO(n)timeandO(1)space?题意：给定一个单向链表，判断是否为回文解决思路：假设一个链表是回文，那么把链表分割为1…n/2,n/2+1…n两个部分，这两个部分肯定是相同的（把第二部分顺序逆转过来或者逆转第一部分）。所以如果我们能把任何一个部
u012403246·2015-08-12 10:00

LeetCode题解：Lowest Common Ancestor of a Binary Search Tree

Givenabinarysearchtree(BST),findthelowestcommonancestor(LCA)oftwogivennodesintheBST.AccordingtothedefinitionofLCAonWikipedia:“ThelowestcommonancestorisdefinedbetweentwonodesvandwasthelowestnodeinTthat
u012403246·2015-08-12 10:00

LeetCode题解：Delete Node in a Linked List

Writeafunctiontodeleteanode(exceptthetail)inasinglylinkedlist,givenonlyaccesstothatnode.Supposedthelinkedlistis1->2->3->4andyouaregiventhethirdnodewithvalue3,thelinkedlistshouldbecome1->2->4aftercalli
u012403246·2015-08-12 10:00

LeetCode题解：Pascal's Triangle II

Givenanindexk,returnthekthrowofthePascal’striangle.Forexample,givenk=3,Return[1,3,3,1].Note:CouldyouoptimizeyouralgorithmtouseonlyO(k)extraspace?题意：返回给定k对应第k行的Pascal三角形解决思路：其实很简单，把Pascal三角形的解决办法改一改就可以
u012403246·2015-08-12 10:00

LeetCode题解：Pascal's Triangle

GivennumRows,generatethefirstnumRowsofPascal’striangle.Forexample,givennumRows=5,Return[[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]题意是：给定一个正整数numRows代表行数，返回对应行数的Pascal三角形。解决这个问题的办法很简单了，根据Pascal三角形的特征计算就可
u012403246·2015-08-12 10:00

[leetcode] 040. Combination Sum II (Medium) (C++)

索引：[LeetCode]Leetcode题解索引(C++/Java/Python/Sql)Github:https://github.com/illuz/leetcode040.CombinationSumII
hcbbt·2015-08-08 08:00

[LeetCode] 039. Combination Sum (Medium) (C++)

索引：[LeetCode]Leetcode题解索引(C++/Java/Python/Sql)Github:https://github.com/illuz/leetcode039.CombinationSum
hcbbt·2015-08-08 08:00

[LeetCode] 038. Count and Say (Easy) (C++/Python)

索引：[LeetCode]Leetcode题解索引(C++/Java/Python/Sql)Github:https://github.com/illuz/leetcode038.CountandSay
hcbbt·2015-07-30 10:00

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·2015-07-18 13:00

LeetCode题解——Longest Palindromic Substring

转自：http://blog.csdn.net/hopeztm/article/details/7932245题目： GivenastringS,findthelongestpalindromicsubstringinS.给出一个字符串S，找到一个最长的连续回文串。例如串 babcbabcbaccba最长回文是:abcbabcba这个题目小弟给出3中解法，前两种的都是O(n^2)，第三种思路是O(
u010025211·2015-07-03 21:00

LeetCode题解——4Median of Two Sorted Arrays

MedianofTwoSortedArraysTherearetwosortedarrays nums1 and nums2 ofsizemandnrespectively.Findthemedianofthetwosortedarrays.TheoverallruntimecomplexityshouldbeO(log(m+n)).1.mergeO(n+m)2.kthsmallestofsort
u010025211·2015-07-03 19:00

LeetCode题解4：Median of Two Sorted Arrays

MedianofTwoSortedArrays问题：求2个有序数组的中位数，要求算法时间复杂度为O(log(m+n))。难度：困难思路：此题为“在2个有序数组中寻找第k个元素”问题的变体。根据中位数的定义，此题可转化为“在2个有序数组中寻找第‘(m+n)/2’个元素”。算法难点在于要求时间复杂度为O(log(m+n))，因此需要充分利用2个数组有序这一条件，每次循环将搜索空间缩小一半。陷阱：数组下
沙札罕·2015-07-02 23:08

LeetCode题解2：Add two numbers

Addtwonumbers问题：给定2个用链表（LinkedList）表示的10进制非负整数，求它们的和。难度：容易思路：遍历2个链表，按位求和。陷阱：进位处理；两个链表长度不同代码：#Definitionforsingly-linkedlist.#classListNode(object):#def__init__(self,x):#self.val=x#self.next=NoneclassS
沙札罕·2015-06-30 18:26
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