问题
I'm supposed to write a program that takes a string of binary code and a number, and outputs all the strings within that hamming distance of the original string. I have a function that does everything, but in the output there are lists within lists. I understand why this is - the function is recursive, and sometimes it will return a list of possible values.
The problem is, I don't know how to change it so it outputs complete strings. For example, for a string of "0000" and hamming distance "2", I get: ["1['100', '010', '001']", "01['10', '01']", "001['1']"]
But what I want is:
1100
1010
1001
0110
0101
0011
Code is below:
def hamming(num, dist):
if dist == 0:
return num
else:
outputlist = list()
for item in range(len(num)):
if len(num[item:]) > dist - 1:
if num[item] == "0":
restoflist = hamming(num[item + 1:], dist - 1)
outputlist.append(num[:item] + "1" + str(restoflist))
else:
restoflist = hamming(num[item + 1:], dist - 1)
outputlist.append(num[:item] + "0" + str(restoflist))
return outputlist
回答1:
If you loop through the list that is returned by hamming
you should be able to append the strings together the right way - like this:
def hamming(num, dist):
if dist == 0:
return num
else:
outputlist = list()
for item in range(len(num)):
if len(num[item:]) > dist - 1:
if num[item] == "0":
restoflist = hamming(num[item + 1:], dist - 1)
if type(restoflist) is not str
for rest in restoflist:
outputlist.append(num[:item] + "1" + str(rest))
else
outputlist.append(num[:item] + "1" + str(restoflist))
else:
restoflist = hamming(num[item + 1:], dist - 1)
if type(restoflist) is not str
for rest in restoflist:
outputlist.append(num[:item] + "0" + str(rest))
else
outputlist.append(num[:item] + "0" + str(restoflist))
return outputlist
回答2:
You can fix it by returning [num]
rather that num
in the base case, and in a general case, combine results from recursive calls using map
and extend
rather than append
:
def hamming(num, dist):
if dist == 0:
return [num]
else:
outputlist = list()
for item in range(len(num)):
if len(num[item:]) > dist - 1:
if num[item] == "0":
restoflist = hamming(num[item + 1:], dist - 1)
outputlist.extend(map(lambda x: num[:item] + "1" + x, restoflist))
else:
restoflist = hamming(num[item + 1:], dist - 1)
outputlist.extend(map(lambda x: num[:item] + "0" + x, restoflist))
return outputlist
>>> hamming('0000', 2)
['1100', '1010', '1001', '0110', '0101', '0011']
>>>
来源:https://stackoverflow.com/questions/22072112/appending-a-list-and-recursion-hamming-distance-python-3