leetcode 解题思路

You would like to make dessert and are preparing to buy the ingredients. You havenice cream base flavors andmtypes of toppings to choose from. You must follow these rules when making your dessert:There must beexactly oneice cream base. You can add...

Given a string that contains only digits0-9and a target value, return all possibilities to addbinaryoperators (not unary)+,-, or*between the digits so they evaluate to the target value.

There are two types of persons:Thegood person: The person who always tells the truth. Thebad person: The person who might tell the truth and might lie.You are given a0-indexed2D integer arraystatementsof sizen x nthat represents the statements ...

You are given therootof abinary treewithnnodes. Each node is uniquely assigned a value from1ton. You are also given an integerstartValuerepresenting the value of the start nodes, and a different integerdestValuerepresenting the value of the d...

You are given an integer arraydigits, where each element is a digit. The array may contain duplicates.You need to findalltheuniqueintegers that follow the given requirements:The integer consists of theconcatenationofthreeelements fromdigitsi...

We havenbuildings numbered from0ton - 1. Each building has a number of employees. It's transfer season, and some employees want to change the building they reside in.You are given an arrayrequestswhererequests[i] = [fromi, toi]represents an empl...

Given a strings,returnthe maximumnumber of unique substrings that the given string can be split into.You can split stringsinto any list ofnon-empty substrings, where the concatenation of the substrings forms the original string.However, you must ...

Given a non-empty 2D arraygridof 0's and 1's, anislandis a group of1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrou...

In a project, you have a list of required skillsreq_skills,and a list ofpeople. The i-th personpeople[i]contains a list of skills that person has.Consider asufficient team: a set of people such that for every required skill inreq_skills, there is...

Given a rectangle of sizenxm, find the minimum number of integer-sided squares that tile the rectangle.Example 1:Input: n = 2, m = 3Output: 3Explanation: 3 squares are necessary to cover the rectangle.2(squares of 1x1)1(square of 2x2)Example ...

Given an Android3x3key lock screen and two integersmandn, where 1 ≤ m ≤ n ≤ 9, count the total number of unlock patterns of the Android lock screen, which consist of minimum ofmkeys and maximumnkeys.Rules for a valid pattern:Each pattern must ...

On a 2-dimensionalgrid, there are 4 types of squares:1represents the starting square. There is exactly one starting square. 2represents the ending square. There is exactly one ending square. 0represents empty squares we can walk over. -1represe...

Given a binary tree where node values are digits from 1 to 9. A path in the binary tree is said to bepseudo-palindromicif at least one permutation of the node values in the path is a palindrome.Return the number ofpseudo-palindromicpaths going from t...

Implement a magic directory withbuildDict, andsearchmethods.For the methodbuildDict, you'll be given a list of non-repetitive words to build a dictionary.For the methodsearch, you'll be given a word, and judge whether if you modifyexactlyone cha...

Given an array of integersnumsand a positive integerk, find whether it's possible to divide this array intoknon-empty subsets whose sums are all equal.Example 1:Input: nums = [4, 3, 2, 3, 5, 2, 1], k = 4Output: TrueExplanation: It's possible...

Given an integer array, your task is to find all the different possible increasing subsequences of the given array, and the length of an increasing subsequence should be at least 2.Example:Input: [4, 6, 7, 7]Output: [[4, 6], [4, 7], [4, 6, 7], [4, 6,

Determine if a Sudoku is valid, according to:Sudoku Puzzles - The Rules.The Sudoku board could be partially filled, where empty cells are filled with the character'.'.A partially filled sud...

Given a time represented in the format "HH:MM", form the next closest time by reusing the current digits. There is no limit on how many times a digit can be reused.You may assume the given input str...

A group of friends went on holiday and sometimes lent each other money. For example, Alice paid for Bill's lunch for $10. Then later Chris gave Alice $5 for a taxi ride. We can model each transaction ...

We can rotate digits by 180 degrees to form new digits. When 0, 1, 6, 8, 9 are rotated 180 degrees, they become 0, 1, 9, 8, 6 respectively. When 2, 3, 4, 5 and 7 are rotated 180 degrees, they become i...

You have 4 cards each containing a number from 1 to 9. You need to judge whether they could operated through*,/,+,-,(,)to get the value of 24.Example 1:Input: [4, 1, 8, 7]Output: TrueExp...

A stringSrepresents a list of words.Each letter in the word has 1 or more options. If there is one option, the letter is represented as is. If there is more than one option, then curly braces de...

Given n unique postive integers, number k (1<=k<=n) and target.Find all possible k integers where their sum is target.ExampleExample 1:Input: [1,2,3,4], k = 2, target = 5Output: [[1,4...

Your are given a binary tree in which each node contains a value. Design an algorithm to get all paths which sum to a given value. The path does not need to start or end at the root or a leaf, but it ...

Given a binary tree, find all paths that sum of the nodes in the path equals to a given numbertarget.A valid path is from root node to any of the leaf nodes.ExampleExample 1:Input:{1,2,4,2,...

Given apatternand a stringstr, find ifstrfollows the same pattern.Herefollowmeans a full match, such that there is abijectionbetween a letter inpatternand anon-emptysubstring instr.(i....

Then-queens puzzle is the problem of placingnqueens on ann×nchessboard such that no two queens attack each other.Given an integern, return all distinct solutions to then-queens puzzle.Each ...

Given a digit string, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telephone buttons) is given below.Input:Digit ...

Given a string s, partition s such that every substring of the partition is a palindrome.Return all possible palindrome partitioning of s.For example, given s = "aab",Return [ ["aa","b"],...

Given two integersnandk. Return all possible combinations ofknumbers out of1, 2, ... , n.ExampleExample 1:Input: n = 4, k = 2Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]Example 2:...

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.Example 1:Input: k = 3...

Given a collection of numbers, return all possible permutations.For example,[1,2,3] have the following permutations:[1,2,3], [1,3,2], [2,1,3], [2,3,1],[3,1,2], and[3,2,1].思路：经典的backtracking. 不要...

Given a collection of integers that might contain duplicates, S, return all possible subsets.Note:Elements in a subset must be in non-descending order. The solution set must not contain dup...

Given a set of distinct integers, S, return all possible subsets.Note:Elements in a subset must be in non-descending order. The solution set must not contain duplicate subsets.For example,If...

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3, a solution set is:"((()))", "(()())", "(())()", "()(())", "()()(...

Follow up for N-Queens problem.Now, instead outputting board configurations, return the total number of distinct solutions.Show TagsHave you met this question in a real int

Write a function to generate the generalized abbreviations of a word.Example:Given word = "word", return the following list (order does not matter):["word", "1ord", "w1rd", "wo1d", "wor1", "

A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59).Each LED represents a zero or one, with the least significant bit o

Given a string S, we can transform every letter individually to be lowercase or uppercase to create another string.  Return a list of all possible strings we could create.Examples:Input: S = "a1b2...

Given an arraynumand a numbertarget. Find all unique combinations innumwhere the numbers sum totarget.ExampleExample 1:Input: num = [7,1,2,5,1,6,10], target = 8Output: [[1,1,6],[1,2,5],[...