Find longest unique substring in string python

Not sure what is wrong in your attempt, but it's complex and in:

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

you're removing elements from a list while iterating on it: don't do that, it gives unexpected results.

Anyway, my solution, not sure it's intuitive, but it's probably simpler & shorter:

• slice the string with an increasing index
• for each slice, create a set and store letters until you reach the end of the string or a letter is already in the set. Your index is the max length
• compute the max of this length for every iteration & store the corresponding string

Code:

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"))

result:

kewamb

Depends on your definition of repeated characters: if you mean consecutive, then the approved solution is slick, but not of characters appearing more than once (e.g.: pwwkewabmb -> 'kewabmb' ).

Here's what I came up with (Python 2):

def longest(word):
    begin = 0
    end = 0
    longest = (0,0)
    for i in xrange(len(word)):
        try:
            j = word.index(word[i],begin,end)
            # longest?
            if end-begin >= longest[1]-longest[0]:
                longest = (begin,end)
            begin = j+1
            if begin==end:
                end += 1
        except:
            end = i+1
    end=i+1
    if end-begin >= longest[1]-longest[0]:
        longest = (begin,end)
    return word[slice(*longest)]

Thus

>>> print longest('pwwkewabmb')
kewabm
>>> print longest('pwwkewambb')
kewamb
>>> print longest('bbbb')
b

My 2-cents:

from collections import Counter

def longest_unique_substr(s: str) -> str:

    # get all substr-ings from s, starting with the longest one
    for substr_len in range(len(s), 0, -1):
        for substr_start_index in range(0, len(s) - substr_len + 1):
            substr = s[substr_start_index : substr_start_index + substr_len]

            # check if all substr characters are unique
            c = Counter(substr)
            if all(v == 1 for v in c.values()):
                return substr

    # ensure empty string input returns ""
    return ""

Run:

In : longest_unique_substr('pwwkewambb')
Out: 'kewamb'

s=input()
ma=0
n=len(s)
l=[]
a=[]
d={}
st=0;i=0
while i<n:
    if s[i] not in d:
        d[s[i]]=i
        l.append(s[i])
    else:
        t=d[s[i]]
        d[s[i]]=i
        s=s[t+1:]
        d={}
        n=len(s)
        if len(l)>=3:
            a.append(l)
            ma=max(ma,len(l))
        l=[];i=-1
    i=i+1
if len(l)!=0 and len(l)>=3:
    a.append(l)
    ma=max(ma,len(l))
if len(a)==0:
    print("-1")
else:
    for i in a:
        if len(i)==ma:
            for j in i:
                print(j,end="")
            break