Given two strings *haystack* and *needle*, return the index of the first occurrence of *needle* in *haystack*, or -1 if *needle* is not part of *haystack*. If *needle* is an empty string, return 0.
First line contains string haystack, second line contains string needle.
Output the index of the first occurrence or -1.
Example 1:
Input:
haystack = "hello" needle = "ll"
Output:
2
Example 2:
Input:
haystack = "aaaaa" needle = "bba"
Output:
-1
Example 3:
Input:
haystack = "" needle = ""
Output:
0
Example 4:
Input:
haystack = "abc" needle = "c"
Output:
2