using recursion to get sub strings in python

Question

how can I use recursion to find the amount of 'a' that is in a string:

example: get_a('halloa') -> 2

here is what I have:

    def get_a(string):
        '''
        return how many times a exist in the string using recursion
        '''
        if string == '':
            return 0
        if string[0] == 'a':
            return 1
    return get_a(string[1:])

@PM2Ring: Maybe it's an exercise in functional-style programming. — Fred Larson
– Fred Larson, Commented Feb 8, 2018 at 15:21
@FredLarson Sure, or at least an exercise in learning about recursion. Otherwise the OP could simply use the .count method. — PM 2Ring
– PM 2Ring, Commented Feb 8, 2018 at 15:25

AndreyF · Accepted Answer · 2018-02-08 15:15:35Z

6

the problem in your code is that you stop the recursion when you find the first a. You'll want to call get_a and collect the as you've already found:

def get_a(string):
    '''
    return how many times a exist in the string using recursion
    '''
    if string == '':
        return 0
    if string[0] == 'a':
        return 1 + get_a(string[1:])
    return get_a(string[1:])

answered Feb 8, 2018 at 15:15

AndreyF

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