ARC是iOS 5推出的新功能，全称叫ARC(AutomaticReferenceCounting)。 简单地说，就是代码中自动加入了retain/release，原先需要手动添加的用来处理内存管理的引用计数的代码可以自动地由编译器完成了。该机制在iOS 5/ Mac OS X 10.7 开始导入，利用 Xcode4.2可以使用该机制。简单地理解ARC，就是通过指定的语法，让编译器(LLVM3.0)在编译代码时，自动生成实例的引用计数管理部分代码。有一点，ARC并不是GC，它只是一种代码静态分析（StaticAnalyzer）工具。
Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length. Do not allocate extra space for another array, you must do this in place with constant memory. For example, Given input array nums = [1,1,2], Your function should return length = 2, with the first two elements of nums being 1 and 2 respectively. It doesn’t matter what you leave beyond the new length.
std::distance template typename iterator_traits::difference_type distance (InputIterator first, InputIterator last); Return distance between iterators Calculates the number of elements between first and last. c++ reference
Remove consecutive duplicates in range Removes all but the first element from every consecutive group of equivalent elements in the range [first,last). c++ reference
题目描述: Suppose a sorted array is rotated at some pivot unknown to you beforehand. (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2). You are given a target value to search. If found in the array return its index, otherwise return -1. You may assume no duplicate exists in the array.
Sending Messages When it encounters a method invocation, the compiler might generate a call to any of several functions to perform the actual message dispatch, depending on the receiver, the return value, and the arguments. You can use these functions to dynamically invoke methods from your own plain C code, or to use argument forms not permitted by NSObject’s perform… methods. These functions are declared in /usr/include/objc/objc-runtime.h.
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objc_msgSend sends a message with a simple return value to an instance of a class.
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objc_msgSend_stret sends a message with a data-structure return value to an instance of a class.
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objc_msgSendSuper sends a message with a simple return value to the superclass of an instance of a class.
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objc_msgSendSuper_stret sends a message with a data-structure return value to the superclass of an instance of a class.
HTTP Live Streaming HTTP Live Streaming（缩写是 HLS）是一个由苹果公司提出的基于HTTP的流媒体网络传输协议。它的工作原理是把整个流分成一个个小的基于HTTP的文件来下载，每次只下载一些。当媒体流正在播放时，客户端可以选择从许多不同的备用源中以不同的速率下载同样的资源，允许流媒体会话适应不同的数据速率。支持的视频流编码为H.264。我们在视频网站上看到的M3U8后缀的播放链接就是使用HLS协议的视频。HLS优点，1、看完一段缓存一段，防止只看一段视频但是把整个视频文件都缓存下来的用户，减少服务器压力和节省流量。2、根据用户网速切换不同的码率，兼顾流程性和清晰度。
AVAsset is an abstract, immutable class used to model timed audiovisual media such as videos and sounds. An asset may contain one or more tracks that are intended to be presented or processed together, each of a uniform media type, including but not limited to audio, video, text, closed captions, and subtitles.
An AVPlayer is a controller object used to manage the playback and timing of a media asset. It provides the interface to control the player’s transport behavior such as its ability to play, pause, change the playback rate, and seek to various points in time within the media’s timeline. You can use an AVPlayer to play local and remote file-based media, such as QuickTime movies and MP3 audio files, as well as audiovisual media served using HTTP Live Streaming.
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AVPlayer是一个控制对象用于管理媒体asset的播放，它提供了相关的接口控制播放器的行为，比如：播放、暂停、改变播放的速率、跳转到媒体时间轴上的某一个点（简单理解就是实现拖动功能显示对应的视频位置内容）。我们能够使用AVPlayer播放本地和远程的媒体文件（使用 HTTP Live Streaming），比如： QuickTime movies 和 MP3 audio files，所以AVPlayer可以满足音视频播放的基本需求。
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AVFoundation的层次
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AVPlayerItem
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AVPlayerItem models the timing and presentation state of an asset played by an AVPlayer object. It provides the interface to seek to various times in the media, determine its presentation size, identify its current time, and much more.
AVPlayerLayer is a subclass of CALayer to which an AVPlayer object can direct its visual output. It can be used as the backing layer for a UIView or NSView or can be manually added to the layer hierarchy to present your video content on screen.
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负责AVPlayer的视频输出展示。
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依赖关系图
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简单使用
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class AVPlayerTestView: UIView {
let view: UIView? = nil
func initPlayerView() {
guard let url = URL.init(string: "http://meipu1.video.meipai.com/5e81c08e-2850-4fbd-bfc4-4ded297f9f1c.mp") else { return }
let asset = AVAsset.init(url: url)
let item = AVPlayerItem.init(asset: asset)
let player = AVPlayer.init(playerItem: item)
let playerLayer = AVPlayerLayer.init(layer: player)
General State Observations: You can use Key-value observing (KVO) to observe state changes to many of the player’s dynamic properties, such as its currentItem or its playback rate. You should register and unregister for KVO change notifications on the main thread. This avoids the possibility of receiving a partial notification if a change is being made on another thread. AVFoundation invokes observeValue(forKeyPath:of:change:context:) on the main thread, even if the change operation is made on another thread.
AVMutableComposition is a mutable subclass of AVComposition you use when you want to create a new composition from existing assets. You can add and remove tracks, and you can add, remove, and scale time ranges.
An AVAssetExportSession object transcodes the contents of an AVAsset source object to create an output of the form described by a specified export preset.
An AVAssetResourceLoader object mediates resource requests from an AVURLAsset object with a delegate object that you provide. When a request arrives, the resource loader asks your delegate if it is able to handle the request and reports the results back to the asset. AVAssetResourceLoader协调来自AVURLAsset的资源请求，你需要实现它的delegate。当收到一个请求时，ResourceLoader询问你的delegate是否能处理并将结果返回给asset。
题目描述: Suppose a sorted array is rotated at some pivot unknown to you beforehand. (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2). You are given a target value to search. If found in the array return its index, otherwise return -1. You may assume no duplicate exists in the array.
Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length. Do not allocate extra space for another array, you must do this in place with constant memory. For example, Given input array nums = [1,1,2], Your function should return length = 2, with the first two elements of nums being 1 and 2 respectively. It doesn’t matter what you leave beyond the new length.
std::distance template typename iterator_traits::difference_type distance (InputIterator first, InputIterator last); Return distance between iterators Calculates the number of elements between first and last. c++ reference
Remove consecutive duplicates in range Removes all but the first element from every consecutive group of equivalent elements in the range [first,last). c++ reference
Sending Messages When it encounters a method invocation, the compiler might generate a call to any of several functions to perform the actual message dispatch, depending on the receiver, the return value, and the arguments. You can use these functions to dynamically invoke methods from your own plain C code, or to use argument forms not permitted by NSObject’s perform… methods. These functions are declared in /usr/include/objc/objc-runtime.h.
objc_msgSend sends a message with a simple return value to an instance of a class.
objc_msgSend_stret sends a message with a data-structure return value to an instance of a class.
objc_msgSendSuper sends a message with a simple return value to the superclass of an instance of a class.
objc_msgSendSuper_stret sends a message with a data-structure return value to the superclass of an instance of a class.
HTTP Live Streaming HTTP Live Streaming（缩写是 HLS）是一个由苹果公司提出的基于HTTP的流媒体网络传输协议。它的工作原理是把整个流分成一个个小的基于HTTP的文件来下载，每次只下载一些。当媒体流正在播放时，客户端可以选择从许多不同的备用源中以不同的速率下载同样的资源，允许流媒体会话适应不同的数据速率。支持的视频流编码为H.264。我们在视频网站上看到的M3U8后缀的播放链接就是使用HLS协议的视频。HLS优点，1、看完一段缓存一段，防止只看一段视频但是把整个视频文件都缓存下来的用户，减少服务器压力和节省流量。2、根据用户网速切换不同的码率，兼顾流程性和清晰度。
AVAsset is an abstract, immutable class used to model timed audiovisual media such as videos and sounds. An asset may contain one or more tracks that are intended to be presented or processed together, each of a uniform media type, including but not limited to audio, video, text, closed captions, and subtitles.
An AVPlayer is a controller object used to manage the playback and timing of a media asset. It provides the interface to control the player’s transport behavior such as its ability to play, pause, change the playback rate, and seek to various points in time within the media’s timeline. You can use an AVPlayer to play local and remote file-based media, such as QuickTime movies and MP3 audio files, as well as audiovisual media served using HTTP Live Streaming.
AVPlayer是一个控制对象用于管理媒体asset的播放，它提供了相关的接口控制播放器的行为，比如：播放、暂停、改变播放的速率、跳转到媒体时间轴上的某一个点（简单理解就是实现拖动功能显示对应的视频位置内容）。我们能够使用AVPlayer播放本地和远程的媒体文件（使用 HTTP Live Streaming），比如： QuickTime movies 和 MP3 audio files，所以AVPlayer可以满足音视频播放的基本需求。
AVFoundation的层次
AVPlayerItem
AVPlayerItem models the timing and presentation state of an asset played by an AVPlayer object. It provides the interface to seek to various times in the media, determine its presentation size, identify its current time, and much more.
AVPlayerLayer is a subclass of CALayer to which an AVPlayer object can direct its visual output. It can be used as the backing layer for a UIView or NSView or can be manually added to the layer hierarchy to present your video content on screen.
负责AVPlayer的视频输出展示。
依赖关系图
简单使用
1
2
3
4
5
6
7
8
9
10
11
class AVPlayerTestView: UIView {
let view: UIView? = nil
func initPlayerView() {
guard let url = URL.init(string: "http://meipu1.video.meipai.com/5e81c08e-2850-4fbd-bfc4-4ded297f9f1c.mp") else { return }
let asset = AVAsset.init(url: url)
let item = AVPlayerItem.init(asset: asset)
let player = AVPlayer.init(playerItem: item)
let playerLayer = AVPlayerLayer.init(layer: player)
General State Observations: You can use Key-value observing (KVO) to observe state changes to many of the player’s dynamic properties, such as its currentItem or its playback rate. You should register and unregister for KVO change notifications on the main thread. This avoids the possibility of receiving a partial notification if a change is being made on another thread. AVFoundation invokes observeValue(forKeyPath:of:change:context:) on the main thread, even if the change operation is made on another thread.
AVMutableComposition is a mutable subclass of AVComposition you use when you want to create a new composition from existing assets. You can add and remove tracks, and you can add, remove, and scale time ranges.
An AVAssetExportSession object transcodes the contents of an AVAsset source object to create an output of the form described by a specified export preset.
An AVAssetResourceLoader object mediates resource requests from an AVURLAsset object with a delegate object that you provide. When a request arrives, the resource loader asks your delegate if it is able to handle the request and reports the results back to the asset. AVAssetResourceLoader协调来自AVURLAsset的资源请求，你需要实现它的delegate。当收到一个请求时，ResourceLoader询问你的delegate是否能处理并将结果返回给asset。
ARC是iOS 5推出的新功能，全称叫ARC(AutomaticReferenceCounting)。 简单地说，就是代码中自动加入了retain/release，原先需要手动添加的用来处理内存管理的引用计数的代码可以自动地由编译器完成了。该机制在iOS 5/ Mac OS X 10.7 开始导入，利用 Xcode4.2可以使用该机制。简单地理解ARC，就是通过指定的语法，让编译器(LLVM3.0)在编译代码时，自动生成实例的引用计数管理部分代码。有一点，ARC并不是GC，它只是一种代码静态分析（StaticAnalyzer）工具。
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+ 。从根到叶的筛选，元素比较次数至多2(k-1)
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