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| Original file line number | Diff line number | Diff line change |
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| # Linked list as Queue | ||
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| <style> | ||
| .md-logo img { | ||
| content: url('/data-structures/linked-list/polyline-light.svg'); | ||
| } | ||
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| :root [data-md-color-scheme=slate] .md-logo img { | ||
| content: url('/data-structures/linked-list/polyline-night.svg'); | ||
| } | ||
| </style> | ||
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| ## Implementation | ||
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| Singly-linked list is not efficient for queue implementation. That's because `enqueue` can happen in \\(O(1)\\) at `head`, but then `dequeue` would require traversing the whole list till reaching the predecessor of `tail`. i.e. \\(O(n)\\). | ||
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| ```python linenums="1" title="queue.py" | ||
| from linkedlist.list import LinkedList | ||
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| class Queue: | ||
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| def __init__(self): | ||
| self._list = LinkedList() | ||
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| @property | ||
| def empty(self): return self._list.empty | ||
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| @property | ||
| def peek(self): return self._list.head | ||
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| def enqueue(self, data: int): | ||
| self._list.append(data) | ||
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| def dequeue(self): | ||
| return self._list.remove_front() | ||
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| ``` | ||
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| ## Unit tests | ||
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| ```python linenums="1" title="test_queue.py" | ||
| from linkedlist.queue import Queue | ||
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| def test_queue_initialization(): | ||
| queue = Queue() | ||
| assert queue.empty | ||
| assert queue.peek is None | ||
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| def test_queue_enqueue(): | ||
| queue = Queue() | ||
| assert queue.empty | ||
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| queue.enqueue(1) | ||
| assert queue.peek == 1 | ||
| assert not queue.empty | ||
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| queue.enqueue(2) | ||
| assert queue.peek == 1 | ||
| assert not queue.empty | ||
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| queue.enqueue(3) | ||
| assert queue.peek == 1 | ||
| assert not queue.empty | ||
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| def test_queue_dequeue(): | ||
| queue = Queue() | ||
| queue.enqueue(1) | ||
| queue.enqueue(2) | ||
| queue.enqueue(3) | ||
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| assert queue.dequeue() == 1 | ||
| assert not queue.empty | ||
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| assert queue.dequeue() == 2 | ||
| assert not queue.empty | ||
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| assert queue.dequeue() == 3 | ||
| assert queue.empty | ||
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| assert queue.dequeue() is None | ||
| assert queue.empty | ||
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| ``` |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,94 @@ | ||
| # Linked list as Stack | ||
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| <style> | ||
| .md-logo img { | ||
| content: url('/data-structures/linked-list/polyline-light.svg'); | ||
| } | ||
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| :root [data-md-color-scheme=slate] .md-logo img { | ||
| content: url('/data-structures/linked-list/polyline-night.svg'); | ||
| } | ||
| </style> | ||
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| ## Implementation | ||
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| This can be implemented even as a singly-linked list, with `push` and `pop` happening at `head`. | ||
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| ```python linenums="1" title="stack.py" | ||
| from typing import Optional | ||
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| from linkedlist.list import LinkedList | ||
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| class Stack: | ||
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| def __init__(self): | ||
| self._list = LinkedList() | ||
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| @property | ||
| def empty(self): return self._list.empty | ||
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| @property | ||
| def top(self) -> Optional[int]: | ||
| return self._list.head | ||
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| def push(self, data: int): | ||
| self._list.prepend(data) | ||
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| def pop(self) -> Optional[int]: | ||
| if self.empty: | ||
| return None | ||
| return self._list.remove_front() | ||
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| ``` | ||
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| ## Unit tests | ||
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| ```python linenums="1" title="test_stack.py" | ||
| import pytest | ||
| from stack.stack import Stack | ||
| from typing import Optional | ||
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| def test_initialize_stack(): | ||
| s = Stack() | ||
| assert s.empty is True | ||
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| def test_push_element_to_stack(): | ||
| s = Stack() | ||
| assert s.top is None | ||
| assert s.empty | ||
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| s.push(3) | ||
| assert s.top is 3 | ||
| assert not s.empty | ||
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| s.push(2) | ||
| assert s.top is 2 | ||
| assert not s.empty | ||
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| s.push(1) | ||
| assert s.top is 1 | ||
| assert not s.empty | ||
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| def test_pop_element_from_stack(): | ||
| s = Stack() | ||
| s.push(3) | ||
| s.push(2) | ||
| s.push(1) | ||
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| assert s.pop() is 1 | ||
| assert not s.empty | ||
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| assert s.pop() is 2 | ||
| assert not s.empty | ||
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| assert s.pop() is 3 | ||
| assert s.empty | ||
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| assert s.pop() is None | ||
| assert s.empty | ||
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| ``` |
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