计算字符串t在字符串s中出现的次数(KMP)

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题意：给出两个字符串s和t，求t在s中出现的个数

思路：用kmp算法，在第一次匹配(t,s)后，如果t的前缀和后缀一样，就可以直接将s移动到与后缀匹配的位置，不必只一位一位的移

代码如下：

def fail(sub_string):    ans = [0] * (len(sub_string) + 1)    for i in range(1, len(sub_string)):        j = ans[i]        while j > 0 and sub_string[i] != sub_string[j]:            j = ans[j]        if sub_string[i] == sub_string[j]:            ans[i + 1] = j + 1        else:            ans[i + 1] = 0    return ansdef count_substring(string, sub_string):    next = fail(sub_string)    cnt = 0    start = 0    length = len(string) - len(sub_string)    i = 0    while i <= length:        while start < len(sub_string) and string[i + start] == sub_string[start]:            start = start + 1        if start == len(sub_string):            cnt = cnt + 1        i = i + start - next[start]        if next[start] == 0:            i = i + 1        start = next[start]    return cntif __name__ == "__main__":    string = input().strip()    sub_string = input().strip()    count = count_substring(string, sub_string)    print(count)

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