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<!-- This is an automatically generated file. --> <Chapter Label="Chapter_Queues_and_Deques"> <Heading>Queues and Deques</Heading> <P/> <Section Label="Chapter_Queues_and_Deques_Section_API"> <Heading>API</Heading> <P/> <ManSection> <Filt Arg="arg" Name="IsQueue" Label="for IsObject"/> <Returns><K>true</K> or <K>false</K> </Returns> <Description> The category of queues. </Description> </ManSection> <ManSection> <Filt Arg="arg" Name="IsDeque" Label="for IsObject"/> <Returns><K>true</K> or <K>false</K> </Returns> <Description> The category of deques. </Description> </ManSection> <ManSection> <Oper Arg="deque, object" Name="PushBack" Label="for IsDeque, IsObject"/> <Description> Add <A>object</A> to the back of <A>deque</A>. </Description> </ManSection> <ManSection> <Oper Arg="deque, object" Name="PushFront" Label="for IsDeque, IsObject"/> <Description> Add <A>object</A> to the front of <A>deque</A>. </Description> </ManSection> <ManSection> <Oper Arg="deque" Name="PopBack" Label="for IsDeque"/> <Returns>object </Returns> <Description> Remove an element from the back of <A>deque</A> and return it. </Description> </ManSection> <ManSection> <Oper Arg="deque" Name="PopFront" Label="for IsDeque"/> <Returns>object </Returns> <Description> Remove an element from the front of <A>deque</A> and return it. </Description> </ManSection> For queues, this is just an alias for PushBack <ManSection> <Oper Arg="queue, object" Name="Enqueue" Label="for IsQueue, IsObject"/> <Description> Add <A>object</A> to <A>queue</A>. </Description> </ManSection> <ManSection> <Oper Arg="queue" Name="Dequeue" Label="for IsQueue, IsObject"/> <Returns>object </Returns> <Description> Remove an object from the front of <A>queue</A> and return it. </Description> </ManSection> <ManSection> <Attr Arg="arg" Name="Capacity" Label="for IsQueue"/> <Description> Allocated storage capacity of <A>queue</A>. </Description> </ManSection> <ManSection> <Attr Arg="arg" Name="Capacity" Label="for IsDeque"/> <Description> Allocated storage capacity of <A>deque</A>. </Description> </ManSection> <ManSection> <Attr Arg="arg" Name="Length" Label="for IsQueue"/> <Description> Number of elements in <A>queue</A>. </Description> </ManSection> <ManSection> <Attr Arg="arg" Name="Length" Label="for IsDeque"/> <Description> Number of elements in <A>deque</A>. </Description> </ManSection> </Section> <Section Label="Chapter_Queues_and_Deques_Section_Deques_implemented_using_plain_l <Heading>Deques implemented using plain lists</Heading> <P/> <Package>datastructures</Package> implements deques using a circular buffer stored in a &GAP; a plain list, wrapped in a positional object (<Ref Sect="Positional Objects" BookName="ref"/>). <P/> The five positions in such a deque <C>Q</C> have the following purpose <P/> <List> <Item><C>Q![1]</C> - head, the index in <C>Q![5]</C> of the first element in the deque</Item> <Item><C>Q![2]</C> - tail, the index in <C>Q![5]</C> of the last element in the deque</Item> <Item><C>Q![3]</C> - capacity, the allocated capacity in the deque</Item> <Item><C>Q![4]</C> - factor by which storage is increased if capacity is exceeded</Item> <Item><C>Q![5]</C> - GAP plain list with storage for capacity many entries</Item> </List> <P/> Global constants <K>QHEAD</K>, <K>QTAIL</K>, <K>QCAPACITY</K>, <K>QFACTOR</K>, and <K>QDATA</K> are bound to reflect the above. <P/> When a push fills the deque, its capacity is resized by a factor of <K>QFACTOR</K> using PlistDequeExpand. A new empty plist is allocated and all current entries of the deque are copied into the new plist with the head entry at index 1. <P/> The deque is empty if and only if head = tail and the entry that head and tail point to in the storage list is unbound. <ManSection> <Func Arg="[capacity, [factor]]" Name="PlistDeque" /> <Returns>a deque </Returns> <Description> Constructor for plist based deques. The optional argument <A>capacity</A> must be a positive integer and is the capacity of the created deque, and the optional argument <A>factor</A> must be a rational number greater than one which is the factor by which the storage of the deque is increased if it runs out of capacity when an object is put on the queue. </Description> </ManSection> <ManSection> <Func Arg="deque, object" Name="PlistDequePushFront" /> <Description> Push <A>object</A> to the front of <A>deque</A>. </Description> </ManSection> <ManSection> <Func Arg="deque, object" Name="PlistDequePushBack" /> <Description> Push <A>object</A> to the back of <A>deque</A>. </Description> </ManSection> <ManSection> <Func Arg="deque" Name="PlistDequePopFront" /> <Returns>object or fail </Returns> <Description> Pop object from the front of <A>deque</A> and return it. If <A>deque</A> is empty, returns <K>fail</K>. </Description> </ManSection> <ManSection> <Func Arg="deque" Name="PlistDequePopBack" /> <Returns>object or fail </Returns> <Description> Pop object from the back of <A>deque</A> and return it. If <A>deque</A> is empty, returns <K>fail</K>. </Description> </ManSection> <ManSection> <Func Arg="deque" Name="PlistDequePeekFront" /> <Returns>object or fail </Returns> <Description> Returns the object at the front <A>deque</A> without removing it. If <A>deque</A> is empty, returns <K>fail</K>. </Description> </ManSection> <ManSection> <Func Arg="deque" Name="PlistDequePeekBack" /> <Returns>object or fail </Returns> <Description> Returns the object at the back <A>deque</A> without removing it. If <A>deque</A> is empty, returns <K>fail</K>. </Description> </ManSection> <ManSection> <Func Arg="deque" Name="PlistDequeExpand" /> <Description> Helper function to expand the capacity of <A>deque</A> by the configured factor. </Description> </ManSection> </Section> <P/> <E>Queues</E> are linear data structure that allow adding elements at the end of the queue, and removing elements from the front. A <E>deque</E> is a <E>double-ended queue</E>; a linear data structure that allows access to objects at both ends.<P/> <P/> The API that objects that lie in <Ref Filt="IsQueue" Label="for IsObject"/> and <Ref Filt="IsDeque" Label="for IsObject"/> must implement the API set out below. <P/> <Package>datastructures</Package> provides <P/> </Chapter> ¤ Dauer der Verarbeitung: 0.27 Sekunden (vorverarbeitet) ¤*© Formatika GbR, Deutschland |
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2026-03-28