Find the longest unique substring in a python string

Question

I am trying to ask an old question (there are many options) to find the longest substring of a string that does not contain duplicate characters. I cannot understand why my attempt does not work properly:

def findLongest(inputStr):
    resultSet = []
    substr = []

    for c in inputStr:
        print ("c: ", c)
        if substr == []:
            substr.append([c])
            continue

        print(substr)
        for str in substr:
            print ("c: ",c," - str: ",str,"\n")
            if c in str:
                resultSet.append(str)
                substr.remove(str)
            else:
                str.append(c)
        substr.append([c])



    print("Result set:")
    print(resultSet)
    return max(resultSet, key=len)

print (findLongest("pwwkewambb"))

When my output falls into the second 'w', it does not iterate over all substr elements. I think I did something stupid, but I don’t understand what it is, so some recommendations will be appreciated! I feel like I'm going to answer a question ...

The beginning of my output:

c:  p
c:  w
[['p']]
c:  w  - str:  ['p']

c:  w
[['p', 'w'], ['w']]
c:  w  - str:  ['p', 'w'] # I expect the next line to say c: w - str: ['w']

c:  k
[['w'], ['w']] # it is like the w was ignored as it is here
c:  k  - str:  ['w']

c:  k  - str:  ['w']
...

---

EDIT:

I replaced the for loop with

for idx, str in enumerate(substr):
    print ("c: ",c," - str: ",str,"\n")
    if c in str:
        resultSet.append(str)
        substr[idx] = []
    else:
        str.append(c)

and he gives the correct result. The only thing is that empty arrays of elements are set with the next character. It seems a little pointless; There must be a better way.

My expected result is kewamb .

.

c:  p
c:  w
[['p']]
c:  w  - str:  ['p']

c:  w
[['p', 'w'], ['w']]
c:  w  - str:  ['p', 'w']

c:  w  - str:  ['w']

c:  k
[[], [], ['w']]
c:  k  - str:  []

c:  k  - str:  []

c:  k  - str:  ['w']

c:  e
[['k'], ['k'], ['w', 'k'], ['k']]
c:  e  - str:  ['k']

c:  e  - str:  ['k']

c:  e  - str:  ['w', 'k']

c:  e  - str:  ['k']
...

Answer 1

from itertools import groupby

s = set() ## for mutable access

''.join(max((list(g) for _, g in groupby('pwwkewambb', key=lambda x: not ((s and x == s.pop()) or s.add(x)))), key=len))
'kewamb'

groupby , , key, lambda x: x. - , ( )

lambda x: not ((s and x == s.pop()) or s.add(x))

, ( , ), , /. ( ) , , , / .

max len , , groupby

:

def longest(x):
     if hasattr(longest, 'last'):
         result = not (longest.last == x)
         longest.last = x
         return result
     longest.last = x
     return True


''.join(max((list(g) for _, g in groupby('pwwkewambb', key=longest)), key=len))
'kewamb'

Answer 2

, , :

    for str in substr:
        print ("c: ",c," - str: ",str,"\n")
        if c in str:
            resultSet.append(str)
            substr.remove(str)

, : , .

, , , , , :

• , set , , set. -

:

def findLongest(s):
    maxlen = 0
    longest = ""
    for i in range(0,len(s)):
        subs = s[i:]
        chars = set()
        for j,c in enumerate(subs):
            if c in chars:
                break
            else:
                chars.add(c)
        else:
            # add 1 when end of string is reached (no break)
            # handles the case where the longest string is at the end
            j+=1
        if j>maxlen:
            maxlen=j
            longest=s[i:i+j]
    return longest

print(findLongest("pwwkewambb"))

:

kewamb