Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Update (2014-11-02):

The signature of the function had been updated to return the index instead of the pointer. If you still see your function signature returns a char * or String, please click the reload button to reset your code definition.

难度系数：

容易

实现

bool isSub(char *str, char *sub)
{
    int len = strlen(sub);
    for (int i = 0; i < len; ++i)
    {
        if (str[i] != sub[i])
            return false;
    }
    return true;
}

int strStr(char *haystack, char * needle) {
    int hlen = strlen(haystack);
    int nlen = strlen(needle);
    if (hlen == nlen && isSub(haystack, needle)) {
        return 0;
    }
    for (int i = 0; i < hlen - nlen + 1; ++i) {
        if (isSub(haystack+i, needle))
            return i;
    }
    return -1;
}