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pythonstringcountsubsequence

Python count a subsequence in a string

My exercise consists in counting a subsequence in a binary string, but I can't use the count method because, for example, if I have the subsequence '00' in the string '10010000', the count method will return '3' but the correct answer is '4'.

I tried this:

def subseq_uguale(stringa,testo,lunghezza):
    f=0
    for i in range(len(testo)-lunghezza+1):
        confronta=''
        for j in range(lunghezza):
            confronta+=testo[i+j]
        if confronta==stringa:
            f+=1
    return f

Where 'lunghezza' is the length of the subsequence, 'testo' is the sequence and 'stringa' is the subsequence. But it takes too much time! How can I solve this?

Solution

  • Try this

    def subseq_uguale(stringa, testo):
    f=0
    for i in range(len(testo)+1-len(stringa)):
        if stringa==testo[i:i+len(stringa)]:
            f+=1
    return f