The KMP string matching algorithm

    Given two strings S, P, S contained in how to determine P? (Assuming a longer string S, P is required to be consecutive characters in S)

    This is the classic string matching problem. Violence match omitted to say, a better solution is to KMP. For a novice, want to learn KMP, it is recommended to see the following two articles:

KMP string matching algorithm (Ruan Yifeng)

From start to finish a thorough understanding of KMP (2014 Nian the August 22)

If you explain in next The second array is not very good, I suggest reading this

[Classic] algorithm --KMP, in-depth explanation to solve the next array

This paper gives the realization of kmp:

int getnext(char *p, int next[])
{
    int len = strlen(p);
    next[0] = -1;
    int k = -1, j = 0;
    while (j < len)
    {
        while (k >= 0 && p[j] != p[k])
        {
            k = next[k];
        }
        k++;
        j++;
        next[j] = k;
    }
    return 0;
}

void kmp(char *s, char *p)
{
    int slen = strlen(s);
    int plen = strlen(p);
    int *next = new int[plen + 1];    // size is plen + 1
    getnext(p, next);
    int i = 0, j = 0;
    while (i < slen)
    {
        while (j >= 0 && s[i] != p[j])
        {
            j = next[j];
        }
        i++;
        j++;
        if (j == plen)
        {
            printf("found substring at index: %d\n", i - j);
            j = next[j];    // to find more matches
        }
    }
    delete [] next;    // do not forget
}

analysis:

    If the text string of length n, the pattern string length is m, then the time matching process complexity is O (n), calculate next count of O (m) time, KMP overall time complexity is O (m + n).

Reference: 

algorithm to find substring in a string (KMP Algorithm)

Reproduced in: https: //www.cnblogs.com/gattaca/p/4723530.html