78 lines
2.1 KiB
Python
78 lines
2.1 KiB
Python
class QueueNode(object):
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def __init__(self, prev, value, nxt):
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self.value = value
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self.next = nxt
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self.prev = prev
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def __repr__(self):
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nval = self.next and self.next.value or None
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pval = self.prev and self.prev.value or None
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return f"[{repr(pval)}, {self.value}, {repr(nval)}]"
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class Queue(object):
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def __init__(self):
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self.begin = None
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self.end = None
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def count(self):
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"""
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Returns number of items.
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Regresa la cantidad de ítems.
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"""
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count = 0
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node = self.begin
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while node:
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count += 1
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node = node.prev
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return count
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def unshift(self):
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"""
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Removes the first item and returns its value.
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Remueve el primer ítem y regresa su valor.
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"""
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if self.begin is None:
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value = None
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else:
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value = self.begin.value
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if self.begin.prev is None:
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self.begin = self.end = None
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else:
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self.begin = self.begin.prev
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self.begin.next = None
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return value
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def shift(self, obj):
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"""
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Appends a new item on the begin of the list.
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Añade un nuevo ítem al inicio de la lista.
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"""
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node = QueueNode(None, obj, self.begin)
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if self.begin is None:
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self.begin = node
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self.end = self.begin
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else:
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self.begin.prev = self.end = node
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def drop(self):
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"""
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Removes the last item and returns its value.
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Remueve el último ítem y regresa su valor.
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"""
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value = self.end and self.end.value or None
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if value:
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if self.end.next is None:
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self.begin = self.end = None
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else:
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self.end = self.end.next
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self.end.prev = None
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return value
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def first(self):
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"""
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Returns value of first item.
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Regresa el valor del primer ítem.
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"""
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return self.begin and self.begin.value or None
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