RW214: Data Structures and Algorithms
L. van Zijl
Department of Computer Science
University of Stellenbosch
CS214 – (1)
RW214: Data Structures and Algorithms
University of Stellenbosch
Bags, Queues, Stacks
Bags
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Best implementation for efficiency?
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Generics – parameterized types
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Type parameters instantiated as reference types, Java maps to
primitives
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Autobox – automatically cast primitive type to wrapper type
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Auto-unboxing – wrapper to primitive
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Iterable collection (foreach)
CS214 – (2)
RW214: Data Structures and Algorithms
University of Stellenbosch
Bags, Queues, Stacks
Bags
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Duplicate items, order immaterial
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Add items, iterate
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Example – lots of numbers, average, std dev
CS214 – (3)
RW214: Data Structures and Algorithms
University of Stellenbosch
Bags, Queues, Stacks
FIFO queue
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FIFO service in order of arrival (queue at P&P)
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Fairness – implementation must preserve relative order
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Enqueue, dequeue
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Example – read numbers from file, get size, dequeue into array
CS214 – (4)
RW214: Data Structures and Algorithms
University of Stellenbosch
Bags, Queues, Stacks
(Pushdown) Stacks
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LIFO service – items processed reverse order of arrival
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Push, pop
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Example: Arithmetic expression evaluator
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How to convert a string to a value (parse, tokens, execute)
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Two stack algorithm, page 129
CS214 – (5)
RW214: Data Structures and Algorithms
University of Stellenbosch
Bags, Queues, Stacks
Implementing collections
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Fixed capacity stack of strings p 133
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Generalize with generics for any data type Item (p 135)
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NOTE! No generic array creation in Java (cast)
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Generalize capacity with array resizing (copy to new array)
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Loitering – orphan
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Iteration (pp 138-141): hasNext, next
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LIFO stack p 141 model for items in array
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NB! Operation time indep of collection size AND space used
constant factor of coll. size
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But resizing on push/pop time rel. to coll. size. Repair by
using linked lists.
RW214: Data Structures and Algorithms
CS214 – (6)
University of Stellenbosch
Bags, Queues, Stacks
Linked Lists
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Recursive data structure of nodes (item+ref)
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Operations: easy to insert/remove at beginning, insert at end
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Traverse list to remove from end, remove/insert before/after
given node
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How to implement stack with linked list (p149)
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How to implement queue with linked list (p151) [first, last ref]
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NOTE! Space prop. to number items in coll., time indep. of
size of coll.
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See p155 for bags and iteration.
CS214 – (7)
RW214: Data Structures and Algorithms
University of Stellenbosch