Ask a question about a string matching problem in Python

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Given a pattern p to be a string, and the target string target, output the total number of patterns in the target string target p will only be number characters and target will only be lower case characters Runtime: 5s Test case: 2≤ 𝑙𝑒𝑛(𝑝)≤10^2 1≤𝑙𝑒𝑛(𝑡𝑎𝑟𝑔𝑒𝑡)≤10^9 Example 1 Input: '112', 'kehaanggrrd' Output: 3 p: 112 target: kehaanggrrd the pattern '112' appears 3 times in the target string kehaanggrrd, which includes 'aan', 'ggr' and 'rrd' Example 2 Input: '7227', 'abbccb' Output: 1 p: 7227 target: abbccb the pattern '7227' appears 1 times in the target string abbccb, which includes 'bccb What I have tried: i am a ngreen in python, our mentor give a assignment and i have not idea about how to solve the problem, Thanks for your help!!!

Posted 21-Sep-23 21:31pm

li wilde

Updated 21-Sep-23 21:44pm

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Dave Kreskowiak 22-Sep-23 9:59am

The person you should be asking is your mentor.

3 solutions

Solution 1

While we are more than willing to help those that are stuck, that doesn't mean that we are here to do it all for you! We can't do all the work, this is part of your grades and it wouldn't be at all fair for us to do it all for you.

So we need you to do the work, and we will help you when you get stuck. That doesn't mean we will give you a step by step solution you can hand in!
Start by explaining where you are at the moment, and what the next step in the process is. Then tell us what you have tried to get that next step working, and what happened when you did.

If you are having problems getting started at all, then this may help: How to Write Code to Solve a Problem, A Beginner's Guide[^]

Posted 21-Sep-23 21:45pm

OriginalGriff

Solution 2

Lots of information at The Python Tutorial — Python 3.10.12 documentation[^]. Or if you really do not understand the question then ask your mentor.

Posted 21-Sep-23 23:19pm

Richard MacCutchan

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User 16071582 · Accepted Answer · 2023-10-07T05:03:00

Python

def compute_next(pattern: str) -> list:
    """
    Compute the 'next' array for the KMP algorithm.

    Args:
        pattern (str): The pattern (substring) for which to compute the 'next' array.

    Returns:
        list: The computed 'next' array.
    """
    next: list = [0] * len(pattern)
    j: int = 0
    for i in range(1, len(pattern)):
        while j > 0 and pattern[i] != pattern[j]:
            j = next[j - 1]
        if pattern[i] == pattern[j]:
            j += 1
        next[i] = j
    return next


def kmp(text: str, pattern: str) -> int:
    """
    Perform the Knuth-Morris-Pratt (KMP) string matching algorithm.

    Args:
        text (str): The input text in which to search for the pattern.
        pattern (str): The substring to search for in the text.

    Returns:
        int: The total number of occurrences of the pattern in the text.
    """
    next = compute_next(pattern)
    count = 0
    j = 0
    for i in range(len(text)):
        dic = {}
        dic[pattern[j]] = text[i]
        while j > 0 and text[i] != dic[pattern[j]]:
            j = next[j - 1]
        if text[i] == dic[pattern[j]]:
            j += 1
        if j == len(pattern):
            count += 1
            j = next[j - 1]
    return count

if you need to run,simply call the KMP function, and the function will return the final count.