leetcode 解题思路

Given an integer arrayarr, remove a subarray (can be empty) fromarrsuch that the remaining elements inarrarenon-decreasing.Returnthe length of the shortest subarray to remove.Asubarrayis a contiguous subsequence of the array.Example 1:Inp...

Given two stringssandt, returntrueifsis asubsequenceoft, orfalseotherwise.Asubsequenceof a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative posit...

Run-length encodingis a compression algorithm that allows for an integer arraynumswith many segments ofconsecutive repeatednumbers to be represented by a (generally smaller) 2D arrayencoded. Eachencoded[i] = [vali, freqi]describes theithsegment o...

Given a strings, returnthe number ofpalindromic substringsin it.A string is apalindromewhen it reads the same backward as forward.Asubstringis a contiguous sequence of characters within the string.Example 1:Input: s = "abc"Output: 3Exp...

Given abinary arraydata, returnthe minimum number of swaps required to group all1’s present in the array together inany placein the array.Example 1:Input: data = [1,0,1,0,1]Output: 1Explanation: There are 3 ways to group all 1's together:[1,1...

You are given two stringsaandbof the same length. Choose an index and split both stringsat the same index, splittingainto two strings:aprefixandasuffixwherea = aprefix+ asuffix, and splittingbinto two strings:bprefixandbsuffixwhereb = b...

Given astringsand an array of integerscostwherecost[i]is the cost ofdeletingthe characteriins.Return the minimum cost of deletionssuch that there are no two identical letters next to each other.Notice that you will delete the chosen charac...

In a stringSof lowercase letters, these letters form consecutive groups of the same character.For example, a string likeS = "abbxxxxzyy"has the groups"a","bb","xxxx","z"and"yy".Call a grouplargeif it has 3 or more characters. We would like...

Given anon-emptystringsand an abbreviationabbr, return whether the string matches with the given abbreviation.A string such as"word"contains only the following valid abbreviations:["word", "1ord", "w1rd", "wo1d", "wor1", "2rd", "w2d", "wo2", "1...

In a string composed of'L','R', and'X'characters, like"RXXLRXRXL", a move consists of either replacing one occurrence of"XL"with"LX", or replacing one occurrence of"RX"with"XR". Given the starting stringstartand the ending stringend, returnT...

In a row of trees, thei-th treeproducesfruit with typetree[i].Youstart at any treeof your choice, then repeatedly perform the following steps:Add one piece of fruit from this tree to your baskets. If you cannot, stop. Move to the next tree to t...

Let's call any (contiguous) subarray B (of A)amountainif the following properties hold:B.length >= 3 There exists some0 < i< B.length - 1such thatB[0] < B[1] < ... B[i-1] < B[i] > B[i+1] > ... > B[B.length - 1](Note th...

Given an array of n integers nums and a target, find the number of index tripletsi, j, k with 0 that satisfy the conditionnums[i] + nums[j] + nums[k] .For example, given nums = [-2, 0, 1, 3], a

This question is about implementing a basic elimination algorithm for Candy Crush.Given a 2D integer arrayboardrepresenting the grid of candy, different positive integersboard[i][j]represent different types of candies. A value ofboard[i][j] = 0repr...

Given a binary array, find the maximum number of consecutive 1s in this array.Example 1:Input: [1,1,0,1,1,1]Output: 3Explanation: The first two digits or the last three digits are consecutive 1s. The maximum number of consecutive 1s is 3.Note

Given the arraynumsconsisting of2nelements in the form[x1,x2,...,xn,y1,y2,...,yn].Return the array in the form[x1,y1,x2,y2,...,xn,yn].Example 1:Input: nums = [2,5,1,3,4,7], n = 3Output: [2,3,5,4,1,7] Explanation: Since x1=2, x2=5, x3=1, y1=3...

Given a string and a string dictionary, find the longest string in the dictionary that can be formed by deleting some characters of the given string. If there are more than one possible results, return the longest word with the smallest lexicographical ord

Compare two version numbersversion1andversion1.Ifversion1>version2return 1, ifversion1version2return -1, otherwise return 0.You may assume that the version strings are non-empty and cont

The count-and-say sequence is the sequence of integers beginning as follows:1, 11, 21, 1211, 111221, ...1is read off as"one 1"or11.11is read off as"two 1s"or21.21is read off as"o

Given an array of characters, compress itin-place.The length after compression must always be smaller than or equal to the original array.Every element of the array should be acharacter(not int) of length 1.After you are donemodifying the input a...

Given two stringss1ands2, write a function to return true ifs2contains the permutation ofs1. In other words, one of the first string's permutations is thesubstringof the second string.Example 1:Input: s1 = "ab" s2 = "eidbaooo"Output: TrueExp...

From any string, we can form asubsequenceof that string by deleting some number of characters (possibly no deletions).Given two stringssourceandtarget, return the minimum number of subsequences ofsourcesuch that their concatenation equalstarget. ...

用circular array去implement queue，这个题目被面到两次了。昨天onsite被问到了。今天看了下正确答案，确实不难，是自己复习不到位。算法就是：用front 和rear分别表示头和尾，最重要的考点就是用count来表示里面有多少个元素。这样 front和rear只需要一直向前走就可以了。每次enqueue和dequeue的时候，都用size，也就是count来...

Given an array consists of non-negative integers, your task is to count the number of triplets chosen from the array that can make triangles if we take them as side lengths of a triangle.Example 1:Input: [2,2,3,4]Output: 3Explanation:Valid combinat

Given an array consists of non-negative integers, your task is to count the number of triplets chosen from the array that can make triangles if we take them as side lengths of a triangle.Example 1:Input: [2,2,3,4]Output: 3Explanation:Valid combinat

有一类题，看起来很像同向双指针，但是不完全是，一般都是求exactly K同向双指针教会了我们如何求at most K, 现在我们要求exactly K. 那么我们可以转换为 exactly K = atMost(K) - atMost(K - 1);这类题有好多，如下：Substrings of size K with K distinct charsGiven a stringsand an intk, return an int representing the number o...

Given an array of integersnumsand an integerk. Asubarrayis calledniceif there arekodd numbers on it.Return the number ofnicesub-arrays.Example 1:Input: nums = [1,1,2,1,1], k = 3Output: 2Explanation: The only sub-arrays with 3 odd number...

Given three integer arraysarr1,arr2andarr3sortedinstrictly increasingorder, return a sorted array ofonlytheintegers that appeared inallthree arrays.Example 1:Input: arr1 = [1,2,3,4,5], arr2 = [1,2,5,7,9], arr3 = [1,3,4,5,8]Output: [1,5]...

Write a function that takes a string as input and reverse only the vowels of a string.Example 1:Given s = "hello", return "holle".Example 2:Given s = "leetcode", return "leotcede".思路：主

Given a stringsand a stringt, check ifsis subsequence oft.You may assume that there is only lower case English letters in bothsandt.tis potentially a very long (length ~= 500,000) string, andsis a short string (<=100).A subsequence of a...

Your friend is typing hisnameinto a keyboard. Sometimes, when typing a characterc, the key might getlong pressed, and the character will be typed 1 or more times.You examine thetypedcharacters of the keyboard. ReturnTrueif it is possible that i...

A valid parentheses string is either empty(""),"(" + A + ")", orA + B, whereAandBare valid parentheses strings, and+represents string concatenation. For example,"","()","(())()", and"(()(()))"are all valid parentheses strings.A valid paren...

A group of two or more people wants to meet and minimize the total travel distance. You are given a 2D grid of values 0 or 1, where each 1 marks the home of someone in the group. The distance is calcu

You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).Follow up:Could you do this in-place?思路：上下左右替换，layer 注意offset = i - first;是算与前面的差距。然后就

Given a string, your task is to count how many palindromic substrings in this string.The substrings with different start indexes or end indexes are counted as different substrings even they consist ...

Given n non-negative integers a1, a2, ...,an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of linei is at (i, ai) and (i, 0). Find

Given the availability time slots arraysslots1andslots2of two people and a meeting durationduration, return theearliest time slotthat works for both of them and is of durationduration.If the...

Given an arrayAof positive integers, call a (contiguous, not necessarily distinct) subarray ofAgoodif the number of different integers in that subarray is exactlyK.(For example,[1,2,3,1,2]ha...

Given a stringsand an intk, return an int representing the number of substrings (not unique) ofswith exactlykdistinct characters. If the given string doesn't havekdistinct characters, return ...

Given asortedarray of integersnumsand integer valuesa,bandc. Apply a quadratic function of the form f(x) =ax2+bx+cto each elementxin the array.The returned array must be insorted or...