问题
I have small python code that implements the quickselect discussed here.
import random
def Quickselect(A, k):
if not A:
return
pivot = random.choice(A)
i = 0
A1 = []
A2 = [] # Two new arrays A1, A2 to store the split lists
for i in range(len(A)):
if A[i] < pivot :
A1.append(A[i])
else:
A2.append(A[i])
if k < len(A1):
return Quickselect(A1, k)
if k > len(A) - len(A2):
return Quickselect(A2, k-(len(A) - len(A2)))
else:
return pivot
pass
def main():
A = [45,1,27,56,12,56,88]
print(Quickselect(A,2))
pass
I seem to be getting an randrange error. Is something amiss?
Edit: Implemented random.choice
instead of random.randint
.
The above code seems to work fine. Thanks to User Blender.
回答1:
Your error occurs because randrange
breaks when the range is empty (i.e. randrange(1, 1)
).
Use random.choice
instead and change k <= len(A1)
to k < len(A1)
:
def quick_select(A, k):
pivot = random.choice(A)
A1 = []
A2 = []
for i in A:
if i < pivot:
A1.append(i)
elif i > pivot:
A2.append(i)
else:
pass # Do nothing
if k <= len(A1):
return Quickselect(A1, k)
elif k > len(A) - len(A2):
return Quickselect(A2, k - (len(A) - len(A2)))
else:
return pivot
来源:https://stackoverflow.com/questions/14659637/python-based-quickselect-implementation-resulting-in-error