KMP算法

#include<iostream>
#include<cstring>
using namespace std;

int* make_pmt(const char *p)   //得到回溯的数组
{
    unsigned int len = strlen(p);
    int *ret = static_cast<int *>(malloc(sizeof(int)*len));
    if (NULL != ret)
    {
        ret[0] = 0;
        int ll = 0;
        for (unsigned int i = 1; i < len; i++)
        {
            while (ll > 0 && p[ll] != p[i])
            {
                ll = ret[ll - 1];
            }
            if (p[ll] == p[i])
            {
                ll++;
            }
            ret[i] = ll;
        }
    }
    return ret;
}

int KMP(const char *s, const char *p)
{
    int ret = -1;
    int sl = strlen(s);
    int pl = strlen(p);
    int *pmt = make_pmt(p);
    for (int i = 0, j = 0; i < sl; i++)
    {
        while ((j > 0) && (s[i] != p[j]))
        {
            j = pmt[j - 1];
        }
        if (s[i] == p[j])
        {
            j++;
        }
        if (j == pl)
        {
            ret = i + 1 - pl;
            break;
        }
    }
    free(pmt);
    return ret;
}
int main()
{
    //测试数据1，如果匹配到了就返回相应的下标，没有匹配到就返回-1
    int n = KMP("abcde","cde");
    cout << n << endl;
    //测试数据2
    n = KMP("abcde", "bcde");
    cout << n << endl;
    return 0;
}