实现strStr()函数

方法一：暴力解法

int strStr(string haystack, string needle) {
    if (needle.empty())
        return 0;

    int M = haystack.size();
    int N = needle.size();

    for (int i = 0; i <= M - N; i++)
    {
        int j;
        for (j = 0; j < N; j++)
        {
            if (needle[j] != haystack[i + j])
            {
                break;
            }
        }
        if (j == N)
            return i;
    }
    return -1;
}

方法二：利用memcmp，一层for循环即可解决

int strStr(string haystack, string needle) {
    if (needle.empty())
        return 0;

    int M = haystack.size();
    int N = needle.size();

    char* m = new char[M + 1];
    char* n = new char[N + 1];

    memcpy(m, haystack.c_str(), M);
    memcpy(n, needle.c_str(),    N);
    m[M] = '';
    n[N] = '';

    for (int i = 0; i <= M - N; i++)
    {
        if (0 == memcmp(&m[i], n, N))
        {
            delete[] m;
            delete[] n;
            return i;
        }
    }

    delete[] m;
    delete[] n;

    return -1;
}

方法三： KMP算法