Linear Data Structures 1.9

Linear Data Structures 1.9 - Queue Example Operation Q...

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Unformatted text preview: Queue Example Operation Q enqueue(5) – (5) enqueue(3) – (5, 3) dequeue() 5 (3) enqueue(7) – (3, 7) dequeue() 3 (7) front() 7 (7) dequeue() 7 () dequeue() “error” () isEmpty() true () enqueue(9) – (9) enqueue(7) – (9, 7) size() 2 (9, 7) enqueue(3) – (9, 7, 3) enqueue(5) – (9, 7, 3, 5) dequeue() CSE 2011 Prof. J. Elder Output 9 (7, 3, 5) - 41 - Last Updated: 12-01-17 9:52 AM Array-Based Queue •  Use an array of size N in a circular fashion •  Two variables keep track of the front and rear f index of the front element r index immediately past the rear element •  Array location r is kept empty normal configuration Q 012 f r wrapped-around configuration Q 012 CSE 2011 Prof. J. Elder r f - 42 - Last Updated: 12-01-17 9:52 AM Queue Operations •  We use the modulo operator (remainder of division) Algorithm size() return (N - f + r) mod N Algorithm isEmpty() return (f = r) Note: N ! f + r = (r + N ) ! f Q 012 f 012 r r Q CSE 2011 Prof. J. Elder f - 43 - Last Updated: 12-01-17 9:52 AM Queue Operations (cont.) •  Operation enqueue may throw an exception if the array is full Algorithm enqueue(o) if size() = N - 1 then throw FullQueueException else Q[r]  o r  (r + 1) mod N Q 012 f 012 r r Q CSE 2011 Prof. J. Elder f - 44 - Last Updated: 12-01-17 9:52 AM Queue Operations (cont.) •  Operation dequeue throws an exception if the queue is empty Algorithm dequeue() if isEmpty() then throw EmptyQueueException else o  Q[f] f  (f + 1) mod N return o Q 012 f 012 r r Q CSE 2011 Prof. J. Elder f - 45 - Last Updated: 12-01-17 9:52 AM ...
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This note was uploaded on 02/14/2012 for the course CSE 2011Z taught by Professor Elder during the Fall '11 term at York University.

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Linear Data Structures 1.9 - Queue Example Operation Q...

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