recursion to find odd numbers in a python list

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recursion to find odd numbers in a python list

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#1 by (2 votes)
#2 by (1 votes)

1

I would like to know how to use recursion in Python to do a function that traverses all oddities in a list and append them to a new list

Tested the code to get a null output. I ran the debugger and still could not find the reason. It stopped on line 14 (last line) and returned null, below the code is the output

My code so far:

def encontra_impares(lista):
    lis = []
    if len(lista) == 1 and lista[0] % 2 == 0:
        if not lista[0] % 2 == 0:
            return lis
        return lista
    else:
        if lista[0] % 2 == 0:
            return lista[0] + encontra_impares(lista[1:])

Output:

>>> encontra_impares([1,2,3])

[DEBUG ON]

>>>

Expected output:

>>> encontra_impares([1,2,3])


>>> '[1,3]'

Debugger:

>'_main_'.encontra_impares(), line 14 if lista[0] % 2 == 0:

python

asked by anonymous 17.07.2017 / 20:25

2 answers

2

def impares(l, i=0, lst_impares=[]):
    try:
        e = l[i] if l[i]%2!=0 else None
        i+=1
        if e:
            lst_impares.append(e)
        return impares(l,i,lst_impares) 
    except:
        return lst_impares

print(impares([1,2,3,4,5,19,10]))
[1, 3, 5, 19]

Run on repl.it

17.07.2017 / 21:06

What is the best way to generate random code that is not repeated in the database? [duplicate] Organize data flow by string pattern

score 1 · Accepted Answer

Doing the Table Test :

def encontra_impares(lista):
    lis = []
    if len(lista) == 1 and lista[0] % 2 == 0:
        if not lista[0] % 2 == 0:
            return lis
        return lista
    else:
        if lista[0] % 2 == 0:
            return lista[0] + encontra_impares(lista[1:])

encontra_impares([1,2,3])

The function encontra_impares is called with lista = [1, 2, 3] ;

Defines a local variable lis = [] ;

Verify that the length of lista is 1 and that the value is even. The length is 3, so run else ;

Checks whether the value in position 0 is even. No, because in position 0 is 1, which is odd, then if is not executed;

End of program?

Now understand why your program apparently crashed and the output is zero? A solution to the problem:

def encontra_impares(lista):

    # Define a lista que armazenará os números ímpares:
    lis = []

    # Verifica se há elementos na lista:
    if len(lista) > 0:

        # Retira o primeiro elemento da lista:
        numero = lista.pop(0)

        # Verifica se o número é ímpar:
        if numero % 2 != 0:

            # Sim, então adiciona-o à lista de ímpares:
            lis.append(numero)

        # Faz a união do resultado atual com o retorno para o resto da lista:
        lis = lis + encontra_impares(lista)

    # Retorna a lista final:
    return lis

See working at Ideone .