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executable file
·55 lines (46 loc) · 1.36 KB
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""" a queue class implemented using Python list
"""
class QueueUnderflow(ValueError):
pass
class SQueue(object):
def __init__(self, init_len=8):
self.len = init_len # length of mem-block
self.elems = [0] * init_len
self.head = 0 # index of head element
self.elnum = 0 # number of elements
def is_empty(self):
return self.elnum == 0
def first(self):
if self.elnum == 0:
raise QueueUnderflow
return self.elems[self.head]
# 出队
def dequeue(self):
if self.elnum == 0:
raise QueueUnderflow
e = self.elems[self.head]
self.head = (self.head + 1) % self.len
self.elnum -= 1
return e
# 入队
def enqueue(self, elem):
if self.elnum == self.len:
self.__extend()
self.elems[(self.head + self.elnum) % self.len] = elem
self.elnum += 1
# 扩张存储区
def __extend(self):
old_len = self.len
self.len *= 2
new_elems = [0] * (self.len)
for i in range(old_len):
new_elems[i] = self.elems[(self.head + i) % old_len]
self.elems, self.head = new_elems, 0
if __name__ == '__main__':
q = SQueue()
for i in range(10):
q.enqueue(i * 3)
print(q.dequeue())
q.enqueue(100)
while not q.is_empty():
print(q.dequeue())