Learning from the mistakes

感想我搜了一下，好像还没有搜到中文博客关于这一题的解题报告，我这里弥补一下空缺。problemThere is a special square room with mirrors on each of the four walls.  Except for the southwest corner, there are receptors on each of the remaining cor...

感想这是我在牛客网上看到的很经典的一个动态规划的题目，我当时也是不怎么懂，这里我把它记录下来，尽量写详细。problemGiven two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 ...

感想这道题在leetcode是hard的难度，通过率只有21.2%，我记得在某次笔试的时候做到了这一道题，那时候做得不怎么好，我这里把记录一下我以前写的代码，就当复习一下题目Design and implement a data structure forLeast Recently Used (LRU) cache. It should support the following ...

DescriptionGiven four lists A, B, C, D of integer values, compute how many tuples (i, j, k, l) there are such that A[i] + B[j] + C[k] + D[l] is zero.To make problem a bit easier, all A, B, C, D have...

DescriptionGiven a sequence of n integers a1, a2, …, an, a 132 pattern is a subsequence ai, aj, ak such that i < j < k and a_i < a_k < a_j. Design an algorithm that takes a list of n numb...

DescriptionGiven a list accounts, each element accounts[i] is a list of strings, where the first element accounts[i][0] is a name, and the rest of the elements are emails representing emails of the a...

DescriptionDesign a data structure that supports the following two operations:void addWord(word)bool search(word)search(word) can search a literal word or a regular expression string containing o...

DescriptionGiven a non-negative integer num, repeatedly add all its digits until the result has only one digit.Example:Input: 38Output: 2 Explanation: The process is like: 3 + 8 = 11, 1 + 1 = 2. ...

DescriptionGiven the root of a binary tree, then value v and depth d, you need to add a row of nodes with value v at the given depth d. The root node is at depth 1.The adding rule is: given a positi...

DescriptionAdditive number is a string whose digits can form additive sequence.A valid additive sequence should contain at least three numbers. Except for the first two numbers, each subsequent numb...

DescriptionWe are given a binary tree (with root node root), a target node, and an integer value K.Return a list of the values of all nodes that have a distance K from the target node. The answer c...

DescriptionWe had some 2-dimensional coordinates, like “(1, 3)” or “(2, 0.5)”. Then, we removed all commas, decimal points, and spaces, and ended up with the string S. Return a list of strings repr...

DescriptionA sequence of number is called arithmetic if it consists of at least three elements and if the difference between any two consecutive elements is the same.For example, these are arithmeti...

DescriptionYou have a total of n coins that you want to form in a staircase shape, where every k-th row must have exactly k coins.Given n, find the total number of full staircase rows that can be fo...

DescriptionA zero-indexed array A of length N contains all integers from 0 to N-1. Find and return the longest length of set S, where S[i] = {A[i], A[A[i]], A[A[A[i]]], … } subjected to the rule belo...

DescriptionWe are given an array asteroids of integers representing asteroids in a row.For each asteroid, the absolute value represents its size, and the sign represents its direction (positive mean...

DescriptionGiven two strings S and T, return if they are equal when both are typed into empty text editors. # means a backspace character.Example 1:Input: S = "ab#c", T = "ad#c"Output: trueExplan...

DescriptionYou’re now a baseball game point recorder.Given a list of strings, each string can be one of the 4 following types:Integer (one round’s score): Directly represents the number of points ...

DescriptionImplement a basic calculator to evaluate a simple expression string.The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division...

DescriptionImplement a basic calculator to evaluate a simple expression string.The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers a...

DescriptionGiven two integers n and k, you need to construct a list which contains n different positive integers ranging from 1 to n and obeys the following requirement:Suppose this list is [a1, a2,...

DescriptionGiven two strings A and B of lowercase letters, return true if and only if we can swap two letters in A so that the result equals B.Example 1:Input: A = "ab", B = "ba"Output: trueExam...

DescriptionThere is a room with n lights which are turned on initially and 4 buttons on the wall. After performing exactly m unknown operations towards buttons, you need to return how many different ...

DescriptionThere are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb. On the third round, you toggle every third bulb (turning on if it’s off or ...

DescriptionYou are playing the following Bulls and Cows game with your friend: You write down a number and ask your friend to guess what the number is. Each time your friend makes a guess, you provid...

DescriptionIn the “100 game,” two players take turns adding, to a running total, any integer from 1…10. The player who first causes the running total to reach or exceed 100 wins.What if we change th...

DescriptionInitially on a notepad only one character ‘A’ is present. You can perform two operations on this notepad for each step:Copy All: You can copy all the characters present on the notepad (p...

DescriptionWe have two special characters. The first character can be represented by one bit 0. The second character can be represented by two bits (10 or 11).Now given a string represented by sever...

DescriptionYour are given an array of integers prices, for which the i-th element is the price of a given stock on day i; and a non-negative integer fee representing a transaction fee.You may comple...

DescriptionSuppose you have a long flowerbed in which some of the plots are planted and some are not. However, flowers cannot be planted in adjacent plots - they would compete for water and both woul...

DescriptionThere are N children standing in a line. Each child is assigned a rating value.You are giving candies to these children subjected to the following requirements:Each child must have at l...

DescriptionN cars are going to the same destination along a one lane road. The destination is target miles away.Each car i has a constant speed speed[i] (in miles per hour), and initial position po...

DescriptionThere are n cities connected by m flights. Each fight starts from city u and arrives at v with a price w.Now given all the cities and flights, together with starting city src and the dest...

DescriptionGiven a positive integer, check whether it has alternating bits: namely, if two adjacent bits will always have different values.Example 1:Input: 5Output: TrueExplanation:The binary re...

DescriptionGiven a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level from leaf to root).For example:Given binary tree [3,9,20,nul...

DescriptionYou are given coins of different denominations and a total amount of money amount. Write a function to compute the fewest number of coins that you need to make up that amount. If that amou...

DescriptionGiven an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.Example:nums = [1, 2, 3]target = 4...

DescriptionGiven two strings representing two complex numbers.You need to return a string representing their multiplication. Note i2 = -1 according to the definition.Example 1:Input: "1+1i", "1+1i...

DescriptionGiven a positive integer N, how many ways can we write it as a sum of consecutive positive integers?Example 1:Input: 5Output: 2Explanation: 5 = 5 = 2 + 3Example 2:Input: 9Output: 3...

DescriptionSay you have an array for which the ith element is the price of a given stock on day i.Design an algorithm to find the maximum profit. You may complete as many transactions as you like (i...