#28 Implement strStr()

题目链接：https://leetcode.com/problems/implement-strstr/

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.

int strStr(char* haystack, char* needle) {
    if(*needle == '\0')
        return 0;
    int index = 0;
    int len1 = strlen(haystack), len2 = strlen(needle);
    while(index <= len1 - len2) {   //母串剩余字符数小于字串时不需要继续遍历；当字串较大时可以节约很多时间
        int i = 0; //从第一个字符开始比较，直到出现不相同字符
        while(haystack[index + i] && needle[i] && haystack[index+i] == needle[i])
            ++i;
        if(needle[i] == '\0')   //找到相同字串则返回
            return index;
        ++index;
    }
    return -1;          //不包含字串则返回-1
}