CODEWITHSUNDEEP
pythonlist
bartukilickaya
bartukilickaya

Reputation: 57

Trying to remove common elements in the list with recursion

My code:

def shorter(lst):
    if len(lst) == 0:
        return []
    if lst[0] in lst[1:]:
        lst.remove(lst[0])
    shorter(lst[1:])
    return lst

print shorter(["c","g",1,"t",1])

Why does it print ["c","g",1,"t",1] instead of ["c","g","t",1]

Upvotes: 0

Views: 114

Answers (2)

davidedb
davidedb

Reputation: 876

A possible recursive solution could be:

def shorter(lst):
    if lst:
        if lst[0] in lst[1:]:
            prefix = []        # Skip repeated item.
        else:
            prefix = [lst[0]]  # Keep unique item.
        return prefix + shorter(lst[1:])
    else:
        return lst

The previous code can also be compacted to:

def shorter(lst):
    if lst:
        return lst[0:(lst[0] not in lst[1:])] + shorter(lst[1:])
    else:
        return lst

and the function body can also be reduced to a one-liner:

def shorter(lst):
    return (lst[0:(lst[0] not in lst[1:])] + shorter(lst[1:])) if lst else lst

or even:

def shorter(lst):
    return lst and (lst[0:(lst[0] not in lst[1:])] + shorter(lst[1:]))

Upvotes: 1

Misha Melnyk
Misha Melnyk

Reputation: 409

For a recursive method, what you can do is check a specific index in the again as you have it. If we remove the current element, we want to stay at the same index, otherwise we want to increase the index by one. The base case for this is if we are looking at or beyond the last element in the array since we don't really need to check it.

def shorter(lst, ind=0):
    if ind >= len(lst)-1: #Base Case
        return lst
    if lst[ind] in lst[ind+1:]:
        lst.pop(ind)
        return shorter(lst,ind)
    return shorter(lst, ind+1)
#Stuff to test the function
import random
x = [random.randint(1,10) for i in range(20)]
print(x)
x = shorter(x)
print(x)

Another way to solve this in a single line is to convert the list into a set and then back into a list. Sets have only unique values, so we can use that property to remove any repeating elements.

import random
x = [random.randint(1,10) for i in range(20)]
print(x)
x = list(set(x)) #Converts to set and back to list
print(x)

Upvotes: 2

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