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que=[" "]*20
head,tail=0,0
for i in range(3):
que[tail]=chr(97+i)
tail+=1
st=["b","c","d","a"]
top=3
while head<tail and top>-1:
if st[top]==que[head]:
head+=1
else:
que[tail]=st[top]
tail+=1
top-=1
print(que[head:tail])
执行该程序段，则输出的结果是（ ）
| A．[’c’，’d’，’c’] | B．[’c’，’c’，’d’] |
| C．[’c’，’’，’d’] | D．[’c’，’d’] |
同类型试题
y = sin x， x∈R， y∈[–1，1]，周期为2π，函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x， x∈[–1，1]， y∈[–π/2，π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
y = sin x， x∈R， y∈[–1，1]，周期为2π，函数图像以 x = (π/2) + kπ 为对称轴
y = arcsin x， x∈[–1，1]， y∈[–π/2，π/2]
sin x = 0 ←→ arcsin x = 0
sin x = 1/2 ←→ arcsin x = π/6
sin x = √2/2 ←→ arcsin x = π/4
sin x = 1 ←→ arcsin x = π/2
