Implement strstr() II

Given a  haystack  String and a  needle  character string , stay  haystack  Find in string  needle  The first place the string appears  ( from 0 Start ). If it doesn't exist , Then return to   -1.

Example  1:

Input : haystack= "hello", needle = "ll"

Output : 2

Example  2:

Input : haystack= "aaaaa", needle = "bba"

Output : -1

explain :

When  needle  When it's an empty string , What value should we return ？ This is a good question in an interview .

For this question , When  needle  When it's an empty string, we should return  0 . This is related to C Linguistic  strstr()  as well as  Java Of  indexOf()  The definition matches .

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resolvent ：

Algorithmic thought ：

primary strstr() function .

strstr(str1,str2)  Function is used to determine the string str2 Whether it is str1 The string of . If it is , Then the function returns str2 stay str1 The address that first appeared in ; otherwise , return NULL.

KMP Algorithm .

Reference resources ：

http://www.ruanyifeng.com/blog/2013/05/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm.html

C++ Code ：