CODEWITHSUNDEEP
python
mchd
mchd

Reputation: 3163

Managing duplicates when sorting by character order in string

I am trying to solve through a challenge where I have to reorder the letters in string s in the order it appears on string t. For example:

For s = "weather" and t = "therapyw", the output should be
sortByString(s, t) = "theeraw";

For s = "good" and t = "odg", the output should be
sortByString(s, t) = "oodg".

This is my code:

def sortByString(s, t):

    s_list = list(s)
    t_list = list(t)
    output = []

    for i in range(len(t_list)):
        if t_list[i] in s_list:
            output.insert(i, t_list[i])

    return ''.join(output)

It works for all cases except if the same letter exists more than once.

s: "weather"
t: "therapyw"
Output:
"theraw"
Expected Output:
"theeraw"

How can I handle this situation in my code above? What am I missing? I appreciate all help but instead of just blurting out the answer, I would like to know what I'm doing wrong.

Upvotes: 0

Views: 60

Answers (3)

LevB
LevB

Reputation: 953

2 steps:

a. create a sorted list of characters in s and their order in t using index()

b. use zip(* to extract the sorted list of characters 

s = "weather"
t = "therapy"

a = sorted([(t.index(c),c) for c in s])
b = ''.join(list(zip(*a))[1])

print(b)

Output:

theeraw

Upvotes: 0

Sarthak Kumar
Sarthak Kumar

Reputation: 304

Easy way

Use enumerate and turn your string into a dict

def sortByString(s, t):

    s_list = list(s)
    t_list = list(t)

    orderdict = {char: index for index, char in enumerate(t_list)}
    output = sorted(list('weather'),key=orderdict.get)

    return ''.join(output)

This will allow repeated values

  • Example
>>> sortByString('weather',"therapyw")
'theeraw'

Modification to OP's code

Just add the element number of times it appear in s to the output 

def sortByString(s,t):
     s_list = list(s)
     t_list = list(t)
     output = []
     for i in range(len(t_list)):
             if t_list[i] in s_list:
                     output.append(t_list[i]*s_list.count(t_list[i]))
     return ''.join(output)
  • output
>>> sortByString('weather',"therapyw")
'theeraw'

Upvotes: 0

Nick
Nick

Reputation: 147166

The issue with your current code is that it only adds one copy of each character in t to output, regardless of how many times it occurs in s. You can work around that by looping over the count of that character in s and appending to output for each count:

def sortByString(s, t):

    s_list = list(s)
    t_list = list(t)
    output = []

    for i in range(len(t_list)):
        for _ in range(s_list.count(t_list[i])):
            output.append(t_list[i])

    return ''.join(output)

print(sortByString('weather',"therapyw"))
print(sortByString('good',"odg"))

Output:

theeraw
oodg

You can simplify the loop by just adding copies of a list with the current character according to the count of the character in s:

for c in t_list:
    output = output + [c] * s_list.count(c)

Upvotes: 1

Related Questions