Articles
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OA - Randomly Choose k Samples
Reservoir sampling is a family of randomized algorithms for randomly choosing k samples from a list of n items, where n is either a very large or unknown number.
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326 - Power of Three
Given an integer, write a function to determine if it is a power of three.
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325 - Maximum Size Subarray Sum Equals k
Given an array nums and a target value k, find the maximum length of a subarray that sums to k. If there isn’t one, return 0 instead.
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Wiggle Sort II
Given an unsorted array nums, reorder it such that nums[0] < nums[1] > nums[2] < nums[3]....(wiggle sort I: nums[0] <= nums[1] >= nums[2] <= nums[3]...)
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323 - Number of Connected Components in an Undirected Graph
Given n nodes labeled from 0 to n - 1 and a list of undirected edges (each edge is a pair of nodes), write a function to find the number of connected components in an undirected graph.
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322 - Coin Change
You 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 amount of money cannot be made up by any combination of the coins, return -1.
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321 - Create Maximum Number
Given two arrays of length m and n with digits 0-9 representing two numbers. Create the maximum number of length k <= m + n from digits of the two. The relative order of the digits from the same array must be preserved. Return an array of the k digits. You should try to optimize your time and space complexity.
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320 - Generalized Abbreviation
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”, “2rd”, “w2d”, “wo2”, “1o1d”, “1or1”, “w1r1”, “1o2”, “2r1”, “3d”, “w3”, “4”]
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Java interview questions
6 Difference Between HashMap And HashTable : Popular Interview Question In Java With Example
Difference Between String , StringBuilder And StringBuffer Classes With Example : Java
Difference Between Arraylist And Vector : Core Java Interview Collection Question
Difference Between Comparable And Comparator Interface Along With Example In Java : Collection
Hashing :How Hash Map Works In Java Or How Get() Method Works Internally
HashMap Vs ConcurrentHashMap : Java Collections Interview Question
Difference Between Iterator And Enumeration With Example : Java Collections Question
Singleton Design Pattern With Example And Program Code
Factory Design Pattern With Example And Program Code
Top 25 Most Frequently Asked Interview Core Java Interview Questions And Answers
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319 - Bulb Switcher
There 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 turning off if it’s on). For the nth round, you only toggle the last bulb. Find how many bulbs are on after n rounds.
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317 - Shortest Distance from All Buildings
You want to build a house on an empty land which reaches all buildings in the shortest amount of distance. You are given a 2D grid of values 0, 1 or 2. The distance is calculated using Manhattan Distance, where distance(p1, p2) = p2.x - p1.x + p2.y - p1.y . -
318 - Maximum Product of Word Lengths
Given a string array words, find the maximum value of length(word[i]) * length(word[j]) where the two words do not share common letters. You may assume that each word will contain only lower case letters. If no such two words exist, return 0.
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Find best container
現在給某個容量(double capacity), 還有一個array(double[] weights), 和int numOfContainers 主要是要在array中選出兩個weights總和小於等於capacity但最接近capacity.然後指定到一個Container object並且return
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Reverse half of a Linkedlist
Reverse the latter half of a linkedlist.
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OA - Flattening a Linked List
Given a linked list where every node represents a linked list and contains two pointers of its type:
- Pointer to next node in the main list (we call it ‘right’ pointer in below code)
- Pointer to a linked list where this node is head (we call it ‘down’ pointer in below code).
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OA - Max multiplication
Given two integer arrays, find the kth smallest multiplication by picking one element from each array.
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OA - String matching
给一个字典，里面全是string，字典很大，可能有几百万个string。然后写一个方法判断输入是否有一个typo，否则返回false。比如，字典有google，facebook，amazon等。输入google返回false，因为没有typo。输入geogle，返回true，因为有一个typo。输入geogla，返回false，因为有多于一个的typo
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Remove Duplicate Letters
Given a string which contains only lowercase letters, remove duplicate letters so that every letter appear once and only once. You must make sure your result is the smallest in lexicographical order among all possible results.
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System design readings
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315 - Count of Smaller Numbers After Self
You are given an integer array nums and you have to return a new counts array. The counts array has the property where counts[i] is the number of smaller elements to the right of nums[i].
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314 - Binary Tree Vertical Order Traversal
Given a binary tree, return the vertical order traversal of its nodes’ values. (ie, from top to bottom, column by column). If two nodes are in the same row and column, the order should be from left to right.
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313 - Super Ugly Number
Write a program to find the nth super ugly number. Super ugly numbers are positive numbers whose all prime factors are in the given prime list primes of size k. For example, [1, 2, 4, 7, 8, 13, 14, 16, 19, 26, 28, 32] is the sequence of the first 12 super ugly numbers given primes = [2, 7, 13, 19] of size 4.
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312 - Burst Balloons
Given n balloons, indexed from 0 to n-1. Each balloon is painted with a number on it represented by array nums. You are asked to burst all the balloons. If the you burst balloon i you will get nums[left] * nums[i] * nums[right] coins. Here left and right are adjacent indices of i. After the burst, the left and right then becomes adjacent. Find the maximum coins you can collect by bursting the balloons wisely.
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Sparse Matrix Multiplication
Given two sparse matrices A and B, return the result of AB.
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290 - Word Pattern
Given a pattern and a string str, find if str follows the same pattern.
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310 - Minimum Height Trees
For a undirected graph with tree characteristics, we can choose any node as the root. The result graph is then a rooted tree. Among all possible rooted trees, those with minimum height are called minimum height trees (MHTs). Given such a graph, write a function to find all the MHTs and return a list of their root labels.
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Asynchronous vs synchronous execution
Explanation 1:
When you execute something synchronously, you wait for it to finish before moving on to another task. When you execute something asynchronously, you can move on to another task before it finishes.
That being, said, in the context of computers this translates into executing a process or task on another "thread." A thread is a series of commands--a block of code--that exists as a unit of work. The operating system can manage multiple threads and assign a thread a piece ("slice") of processor time before switching to another thread to give it a turn to do some work. At its core (pardon the pun), a processor can simply execute a command--it has no concept of doing two things at one time. The operating system simulates this by allocating slices of time to different threads.
Now, if you introduce multiple cores/processors into the mix, then things CAN actually happen at the same time. The operating system can allocate time to one thread on the first processor, then allocate the same block of time to another thread on a different processor.
All of this is about allowing the operating system to manage the completion of your task while you can go on in your code and do other things. Asynchronous programming is a complicated topic because of the semantics of how things tie together when you can do them at the same time. There are numerous articles and books on the subject; have a look!
Explanation 2:
As an aside, I should mention that technically, the concept of synchronous vs. asynchronous really does not have anything to do with threads. Although, in general, it would be unusual to find asynchronous tasks running on the same thread, it is possible, (see below for e.g.) and it is common to find two or more tasks executing synchronously on separate threads... This concept has to do solely with whether or not a second or subsequent task can be initiated until the other task has completed, and that is all. What thread (or threads), or processes, or CPUs, or indeed, what hardware the task[s] are executed on is not relevant.
ASYNCHRONOUS EXAMPLE. In solving many engineering problems, the software is designed to split up the overall problem into multiple individual tasks, and then execute them asynchronously. Inverting a matrix, or a finite element analysis problem, are good examples. In computing, sorting a list is an example. The quick sort routine, for example, splits the list into two lists, and sorts each of them by calling itself recursively. In both of the above examples, the two tasks can (and often were) executed asynchronously. They do not need to be on separate threads. Even a machine with one CPU, and only one thread of execution can be coded to initiate processing of a second task before a first one has completed. The only criterion is that the results of one task are not necessary as inputs to the other task. As long as the start and end times of the tasks overlap, (possible only if the output of neither is needed as inputs to the other), they are being executed asynchronously, no matter how many threads are in use.
SYNCHRONOUS EXAMPLE. Any process consisting of multiple tasks where the tasks must be executed in sequence, but one must be executed on another machine (Fetch and/or update data, get a stock quote from a financial service, etc.). If it's on a separate machine it is on a separate thread, whether synchronous or asynchronous.
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309 - Best Time to Buy and Sell Stock with Cooldown
Say 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 (ie, buy one and sell one share of the stock multiple times) with the following restrictions: You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again). After you sell your stock, you cannot buy stock on next day. (ie, cooldown 1 day) reference
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308 - Range Sum Query 2D - Mutable
Given a 2D matrix matrix, find the sum of the elements inside the rectangle defined by its upper left corner (row1, col1) and lower right corner (row2, col2).
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340 - Longest Substring with At Most K Distinct Characters
Given a string s, find the length of the longest substring T that contains at most k distinct characters.
