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50 lines
1.4 KiB
Markdown
50 lines
1.4 KiB
Markdown
## queues
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<br>
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* first in, first out structures (FIFO), i.e., items are removed at the same order they are added.
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* queues can be implemented with two arrays or a dynamic array (linked list), as long as items are added and removed from opposite sides.
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* if implemented with a dynamic array, a more efficient solution is to use a circular queue (ring buffer), i.e. a fixed-size array and two pointers to indicate the starting and ending positions. an advantage of circular queues is that we can use the spaces in front of the queue. in a normal queue, once the queue becomes full, we cannot insert the next element even if there is a space in front of the queue. but using the circular queue, we can use the space to store new values.
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* queues are often used in breath-first search (where you store a list of nodes to be processed) or when implementing a cache.
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<br>
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----
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### examples
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<br>
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#### `queues.py`
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<br>
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```python
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> python3 queues.py
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🧪 Testing Queue...
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Is the queue empty? True
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Adding 1 to 10 in the queue...
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Queue: [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
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Queue size: 10
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Queue peek : 1
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Is the queue empty? False
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Dequeue...
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Queue: [10, 9, 8, 7, 6, 5, 4, 3, 2]
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Queue size: 9
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Queue peek: 2
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Is the queue empty? False
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🧪 Testing Priority Queue...
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Priority Queue: [(-4, 1, Item 4), (-1, 0, Item 1), (-3, 2, Item 3)]
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Pop: Item 4
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Priority Queue: [(-3, 2, Item 3), (-1, 0, Item 1)]
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```
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<br>
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