A website with a large archive of nicely written articles on different topics. A website with amazing in-depth wiki-like writeups on many topics. Notes - HackerEarth. A great crowdsourcing platform for tutorials. Contains several training pages on its website which are designed to develop one's skills in programming solutions to difficult and varied algorithmic problems at one's own pace.
Competitive Programming - Commonlounge. Short video tutorials for beginner and intermediate concepts. An international journal focused on the research and practice of professionals who are working in the field of teaching and learning informatics to talented student.
A Russian website devoted to algorithms of all sorts. One of the most popular tutorial websites among the Taiwanese competitive programming community. Papers from the Chinese IOI training camps. Mini-Editorials , by Mostafa Saad Ibrahim trainees.
OI Wiki is committed to being a free and open continuously updated programming competition competitive programming knowledge integration site.
This wiki is a sort of companion or guide for the competitive programmer who's trying to learn something. Code Monk , by HackerEarth. Codechef's Indian Programming Camp. Lectured by Prof. Competitive Programming , by Steven and Felix Halim.
This book contains a collection of relevant data structures, algorithms, and programming tips. This book includes more than programming challenges, as well as the theory and key concepts necessary for approaching them.
Competitive Programmer's Handbook , by Antti Laaksonen. This book is free for download pdf. An absolutely phenomenal book. An old-time classic. Introduction to Algorithms , by Thomas H. Rivest and Clifford Stein. Also known as CLRS taken from name initials , this book is often referred to as the "bible" for algorithms and data structures. This book revolves around techniques for designing algorithms.
The book is written in more readable text. Algorithms , by Robert Sedgewick and Kevin Wayne. This book is neatly categorized, coupled with elaborate explanations and fantastic illustrations. This book provides a different approach to algorithms, balancing theory with a more practical angle, with a section per-chapter focusing on how to apply algorithms to real-world use cases that can be found in your daily work, or in competitive programming; it also presents a blend of classic, advanced, and new algorithms.
Algorithms , by Jeff Erickson. A free electronic version of a self-published textbook licensed under CC by 4. Discrete Mathematics is closely relevant to competitive programming. Knuth, Oren Patashnik. The book offers a deeper insight into Discrete Mathematics with more emphases on number-related topics.
The book does a brilliant job at bridging the gap between a physical system for scientists and engineers and an abstract system for mathematicians. Introduction to Probability , by Charles M. Laurie Snell. This is a well-written introductory probabilities book. Topics in counting and probability byformer USA Mathematical Olympiad winner David Patrick , topics include inclusion-exclusion, correspondences, the Pigeonhole Principle, constructive expectation, Fibonacci and Catalan numbers, recursion, conditional probability, generating functions, graph theory, and much more..
Codeforces is one of, if not, the most popular contest platforms out there. Topcoder has been around since Google Code Jam is certainly one of the most highly-esteemed programming competitions. AtCoder is a new but phenomenal contest platform created by a team of highly-rated Japanese competitive programmers. CodeChef is a non-profit educational initiative of Directi.
The SPOJ platform is centered around an online judge system. Timus Online Judge is the largest Russian archive of programming problems with automatic judging system. Aizu online judge is a contest platform and problem archive hosted by The University of Aizu. HackerRank is a company that focuses on competitive programming challenges for both consumers and businesses. POJ is an online judge with many great problems maintained by Peking University. Project Euler features a stunning set of good math problems.
HackerEarth is a startup technology company based in Bangalore, India that provides recruitment solutions. New in the competitive programming scene, CS Academy is a growing online judge that hosts competitions once every two weeks.
Programming competitions powered by Mail. CodeFights is a website for competitive programming practice and interview preparation. OmegaUp is a community-based website for competitive programing training. UVa Online Judge. Topcoder problem archive. Programming Contest Calendar - HackerRank. Coding Calendar Android App. Competitive Programming Contests Calendar.
For quick answers, Codeforces is definitely the go-to place to ask about anything competition-related. Competitive Programming - Quora. You would typically get more elaborate answers on Quora, but you might not have your questions answered straightaway. Theoretical Computer Science Stack Exchange. CodeLibrary , by Andrey Naumenko indy A notebook with some advanced data structures and algorithms including some from the China informatics scene.
A good notebook by Igor Naverniouk who is currently a software engineer at Google and part of the Google Code Jam team. How to read input in Java — tutorial - Codeforces. Learn how to read input faster. This is a must-read for those who intend to use Java for competitive programming.
A1: Data can be defined with the characteristics like — data should be traceable, atomic, clear, concise and accurate. A2: Data type is a procedure to classify various types of data. This determines the values that can be used with the corresponding type of operations and data.
Mainly, data types are of two types — Derived data type and built in data type. Average rating 4. In this article, students will find Python Lecture Notes Pdf Download, study material, including the required resources to study Python, and be able to go over important concepts.
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All of this material provided is more to update than the regular B. Tech Notes that are available online. Students can achieve the best grades by using these Python Handwritten Notes Pdf Free Download to study as it can provide for thorough preparation. The following events are generated automatically by the SCXML implementation under conditions defined elsewhere in this document. To simplify the following definitions, we introduce the event NULL.
NULL has no name and is used only in these definitions. All other events have names and are distinct from NULL. In effect, NULL is a pseudo-event that is used in these definitions as a trigger for eventless transitions. A transition is enabled by NULL in atomic state S if a T lacks an 'event' attribute, and b T's source state is S or an ancestor of S and c T lacks an 'cond' attribute or its 'cond' attribute evaluates to "true".
Note that such a transition can never be enabled by any named event. The effective target state s of the transition is the state or set of states specified by its 'target' attribute, with any history states being replaced by the corresponding stored state configuration or default stored state configuration.
The complete target set of a transition consists of all the states that will be active after the transition is taken. Any state whose child ren are added to the complete target set by clause 2 is called a default entry state. If the transition does not contain a 'target', its exit set is empty. Otherwise i. Otherwise, if the transition has 'type' "internal", its source state is a compound state, and all its target states are proper descendants of its source state, the exit set consists of all active states in C that are proper descendants of its source state.
If a transition has 'type' of "internal", but its source state is not compound or its target states are not all proper descendants of its source state, its exit set is defined as if it had 'type' of "external". The exit set of a set of transitions is the union of the exit sets of the individual transitions. If a transition does not contain a 'target', its entry set is empty.
Otherwise, it consists of all members of the transition's complete target set that that are not currently active or are in the exit set. Thus the entry set consists of all members of the transition's complete target set that will not be active once the states in the exit set have been exited.
The entry set of a set of transitions is the union of the entry sets of the individual transitions. If two transitions conflict, then taking them both may lead to an illegal configuration. Hence, only one of the transitions may safely be taken. In order to resolve conflicts between transitions, we assign priorities to transitions as follows: let transitions T1 and T2 conflict, where T1 is optimally enabled in atomic state S1, and T2 is optimally enabled in atomic state S2, where S1 and S2 are both active.
We say that T1 has a higher priority than T2 if a T1's source state is a descendant of T2's source state, or b S1 precedes S2 in document order. It MUST then execute the executable content contained in the transitions in document order. It MUST then enter the states in the transitions' entry set in entry order. Then it MUST cancel any ongoing invocations that were triggered by that state.
If the set is not empty, it MUST execute it as a microstep. If the set is empty, the Processor MUST remove events from the internal event queue until the queue is empty or it finds an event that enables a non-empty optimal transition set in the current configuration.
If it finds such a set, the processor MUST then execute it as a microstep. Otherwise the internal event queue is empty and the Processor has completed a macrostep.
Then the Processor MUST remove events from the external event queue, waiting till events appear if necessary, until it finds one that enables a non-empty optimal transition set in the current configuration. Note that Such system generated IDs cannot normally be referenced elsewhere in the document because they are not known to the author.
In particular, a state with a system generated ID cannot be the target of a transition. Furthermore the attribute 'idlocation' can be used to capture this automatically generated id.
Executable content allows the state machine to do things. It provides the hooks that allow an SCXML session to modify its data model and interact with external entities. Executable content consists of actions that are performed as part of taking transitions. This standard defines elements of executable content which can raise events 4. In addition, SCXML implementations are allowed to define their own, platform-specific executable content see 4. Note that the event will not be processed until the current block of executable content has completed and all events that are already in the internal event queue have been processed.
This order depends on the data model in use. For each item in turn, the processor MUST assign it to the item variable. Note that the assigned value MAY be null or undefined if the collection contains a null or undefined item. It MUST then proceed to the next item in iteration order.
The manner in which the message is displayed or logged is platform-dependent. The following elements of executable content are defined elsewhere in this specification. Wherever executable content is permitted, an arbitrary number of elements MAY occur. Such a sequence of elements of executable content is called a block. The execution of other blocks of executable content is not affected. Events raised during the processing of executable content are treated like any other events.
Note in particular, that error events will not be removed from the queue and processed until all events preceding them in the queue have been processed. Implementations MAY provide additional executable content corresponding to special features of their implementations. The functionality of such platform-specific content is not restricted, except that it MUST NOT cause transitions or any form of change of state except indirectly, by raising events that trigger transitions.
Note that SCXML treats the executable content triggered by a transition as a single blocking operation and that no events are processed until all the executable content has completed. It is thus important that all executable content, including platform-specific extensions, execute swiftly.
Note that the schema E Schema allows elements from arbitrary namespaces inside blocks of executable content. See A. The Data Model offers the capability of storing, reading, and modifying a set of data that is internal to the state machine. Implementations may choose the set of data models that they support.
In addition to the underlying data structure, the data model defines a set of expressions as described in 5. These expressions are used to refer to specific locations in the data model, to compute values to assign to those locations, and to evaluate boolean conditions.
Finally, the data model includes a set of system variables, as defined in 5. The data model is defined via the 5. These values may be specified in-line or loaded from an external source. They can then be updated via the 5. The 5. Finally, the 5. The interpretation of these elements depends on the data model in question, and not all elements are supported in all data models.
For the details of specific data models, see B Data Models. The exact nature of the data object depends on the data model language used. The manner in which the environment specifies these overriding values is platform-dependent. Note that in the latter two cases, the interpretation of the object or content will depend on the data model. See B Data Models for details. Implementations MAY predeclare and predefine variables in the data model.
In particular, no means is defined for external entities to modify the data model. However in some deployments it may be possible for external entities to modify the data model. For example, if SCXML is implemented in JavaScript in a browser, the scope of a document's data model is always accessible through the main window object and thus JavaScript code elsewhere in the window can modify the data model independent of the SCXML interpretation algorithm.
Such a situation can lead to race conditions and unpredictable behavior. The value of the data element between the time it is created and the time its parent state is first entered will depend on the data language chosen.
The initial value specified by 'expr', 'src' or in-line content will be assigned to the data element even if the element already has a non-null value when the parent state is first entered. Assignment to a data model is done by using a location expression to denote the part of the data model where the insertion is to be made.
If the location expression does not denote a valid location in the data model or if the value specified by 'expr' or children is not a legal value for the location specified, the SCXML Processor MUST place the error 'error. Note that the nature of the insertion and the definition of a legal value depends on the data model language used.
The exact format of that data will be determined by the data model see B Data Models for details. If the script can not be downloaded within a platform-specific timeout interval, the document is considered non-conformant, and the platform MUST reject it.
For an example of a data model incorporating scripting, see B. SCXML contains three types of expressions, as described below. Different data models will support different languages for these expression types, but certain properties of the expressions are constant across languages and are defined here. Such behavior is defined by the data expression language in use. The set of operators in conditional expressions varies depending on the data model, but all data models MUST support the 'In ' predicate, which takes a state ID as its argument and returns true if the state machine is in that state.
This predicate allows coordination among parallel regions. Location expressions are used to specify a location in the data model, e. The exact nature of a location depends on the data model. A data model definition contains a specification of the underlying data structure. Such a specification of the data structure implicitly defines a set of "legal data values", namely the objects that can be part of such a data structure. In conjunction with this, the data model definition specifies a set of value expressions which can be evaluated at runtime to return legal data values.
If the processor waits until it evaluates the expressions at runtime to raise errors, it MUST raise errors caused by expressions returning illegal values at the points at which the expressions are to be evaluated. Note that this requirement holds even if the implementation is optimizing expression evaluation. We refer to the items in this special part of the data model as 'system variables'.
The set of system variables may be expanded in future versions of this specification. The concrete realization of these variables in a specific data model depends on the language used. The External Communications capability allows an SCXML session to send and receive events from external entities, and to invoke external services.
The 'delay' attribute allows for deferred event delivery and can be used to implement a timer. Each implementation will support one or more such processor, and the author of the SCXML markup can choose the one that is appropriate for the type of endpoint he is trying to reach. When parallel states invoke the same external service concurrently, separate instances of the external service will be started.
They can be distinguished by ids which are associated with them. Similarly, the ids contained in the events returned from the external services can be used to determine which events are responses to which invocation. The finalize code can thus be thought of as a preprocessing stage that applies before the event is added to the event queue. Note that the event will be passed to all parallel states to check for transitions. Since an invocation will be canceled when the state machine leaves the invoking state, it does not make sense to start an invocation in a state that will be exited immediately.
If any such enabled transition is found , it is taken and the state is exited immediately, without triggering the invocation. Thus invocations are triggered only when the state machine has reached a stable configuration, i. It MUST dispatch the message only when the delay interval elapses. Note that the evaluation of the send tag will return immediately. The target is defined by either the 'target' or the 'targetexpr' attribute. If the value of the 'target' or 'targetexpr' attribute is not supported or invalid, the Processor MUST place the error error.
Processors MAY define short form notations as an authoring convenience e. Note that the document author can specify the message content in one of two mutually exclusive ways:. Note that the absence of any error events does not mean that the event was successfully delivered to its target, but only that the platform was able to dispatch the event.
In the rest of this document, we will refer to this identifier as the "invokeid", regardless of whether it is specified by the author or generated by the platform. The automatically generated identifier MUST have the form stateid. Note that the invoked service may ignore some or all of the data passed to it. The service instance MAY be local or remote.
In addition to the explicit arguments, the Processor MUST keep track of the unique invokeid and ensure that it is included in all events that the invoked service returns to the invoking session. All the fields specified in 5. The external service MAY return multiple events while it is processing. Once the external service has finished processing it MUST return a special event 'done. The invoked and invoking process can also communicate via events.
In addition to automatic forwarding specified by the 'autoforward' attribute. In this case, the unique invoke identifier has been stored in the data model location MyInvoke.
Since the target attribute is an expression which is evaluated, the following code will extract that identifier and send a message to the invoked VoiceXML session:. This content is applied before the system looks for transitions that match the event. In the case of parallel states, only the finalize code in the original invoking state is executed.
The Processor MUST execute them right before the event is pulled off the external event queue for processing. In the example below, a state machine using an ECMAScript data model invokes a clock object that returns the current time in a ping event with an XML payload that includes the currentSecond, currentMinute, currentHour , and an isAm flag. The data model includes the underlying data structure plus languages for boolean expressions, location expressions, value expressions, and scripting.
The intent is to ensure interoperability among all processors that support ECMAScript, and all those that support XPath, without requiring all implementations to support either of those data model languages. The value "null" for the 'datamodel' attribute results in an absent or empty data model. In particular:. The boolean expression language consists of the In predicate only. It has the form 'In id ', where id is the id of a state in the enclosing state machine. The predicate MUST return 'true' if and only if that state is in the current state configuration.
Otherwise the Processor MUST treat the content as a space-normalized string literal and assign it as the value of the variable. Similarly, the processor MUST assign the specified initial values to data elements only when the state containing them is first entered, but MAY do so in any order it chooses. Here is an example of its use, taken from G. The following example illustrates this usage.
If it didn't, the Processor would raise error. In cases where this specification does not specify a value for one of these fields or states that the field is empty or has no value, the Processor MUST set the value to ECMAScript undefined.
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