Add queue (#20)

* add queue

* queue example

* Formatted with psf/black

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: realDuYuanChao

basics/deque_example.py

@@ -0,0 +1,28 @@
+def main() -> None:
+    """
+    >>> from collections import deque
+    >>> queue = deque(["Python", "Java", "C"])
+    >>> len(queue)
+    3
+    >>> queue
+    deque(['Python', 'Java', 'C'])
+    >>> queue.popleft()
+    'Python'
+    >>> queue.popleft()
+    'Java'
+    >>> queue.clear()
+    >>> len(queue)
+    0
+    >>> queue
+    deque([])
+    >>> queue.popleft()
+    Traceback (most recent call last):
+    ...
+    IndexError: pop from an empty deque
+    """
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()

data_structures/queue/queue.py

@@ -0,0 +1,131 @@
+"""
+https://en.wikipedia.org/wiki/Queue_(abstract_data_type)
+"""
+from typing import Any
+
+
+class Queue:
+    def __init__(self) -> None:
+        self.queue = []
+
+    def __len__(self) -> int:
+        """
+        >>> queue = Queue()
+        >>> len(queue)
+        0
+        >>> for i in range(0, 5):
+        ...     assert len(queue) == i
+        ...     queue.enqueue(i)
+        >>> len(queue)
+        5
+        """
+        return len(self.queue)
+
+    def __str__(self) -> str:
+        """
+        >>> queue = Queue()
+        >>> str(queue)
+        ''
+        >>> for i in range(1, 6):
+        ...     queue.enqueue(i)
+        >>> str(queue)
+        '1 <- 2 <- 3 <- 4 <- 5'
+        """
+        return " <- ".join([str(item) for item in self.queue])
+
+    def size(self) -> int:
+        """
+        >>> queue = Queue()
+        >>> queue.size()
+        0
+        >>> for i in range(0, 5):
+        ...     assert queue.size() == i
+        ...     queue.enqueue(i)
+        >>> queue.size()
+        5
+        """
+        return len(self)
+
+    def is_empty(self) -> bool:
+        """
+        >>> queue = Queue()
+        >>> queue.is_empty()
+        True
+        >>> queue.enqueue('a')
+        >>> queue.enqueue('b')
+        >>> queue.is_empty()
+        False
+        """
+        return len(self) == 0
+
+    def enqueue(self, item: Any) -> None:
+        """
+        >>> queue = Queue()
+        >>> str(queue)
+        ''
+        >>> for i in range(0, 5):
+        ...     queue.enqueue(i)
+        >>> str(queue)
+        '0 <- 1 <- 2 <- 3 <- 4'
+        """
+        self.queue.append(item)
+
+    def dequeue(self) -> Any:
+        """
+        >>> queue = Queue()
+        >>> for i in range(0, 5):
+        ...     queue.enqueue(i)
+        >>> str(queue)
+        '0 <- 1 <- 2 <- 3 <- 4'
+        >>> queue.dequeue()
+        0
+        >>> queue.dequeue()
+        1
+        >>> str(queue)
+        '2 <- 3 <- 4'
+        >>> for i in range(2, 5):
+        ...     assert queue.dequeue() == i
+        >>> str(queue)
+        ''
+        """
+        if self.is_empty():
+            raise IndexError("dequeue from empty queue")
+        ret_item = self.queue[0]
+        self.queue = self.queue[1:]
+        return ret_item
+
+    def peek(self) -> Any:
+        """
+        >>> queue = Queue()
+        >>> queue.enqueue("Python")
+        >>> queue.enqueue("Java")
+        >>> queue.enqueue("C")
+        >>> queue.peek()
+        'Python'
+        >>> queue.dequeue()
+        'Python'
+        >>> queue.dequeue()
+        'Java'
+        """
+        if self.is_empty():
+            raise IndexError("dequeue from empty queue")
+        return self.queue[0]
+
+    def clear(self) -> None:
+        """
+        >>> queue = Queue()
+        >>> for i in range(1, 6):
+        ...     queue.enqueue(i)
+        >>> str(queue)
+        '1 <- 2 <- 3 <- 4 <- 5'
+        >>> queue.clear()
+        >>> str(queue)
+        ''
+        """
+        self.queue = []
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()