Implement strStr().
+ +Given two strings needle and haystack, return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Clarification:
+ +What should we return when needle is an empty string? This is a great question to ask during an interview.
For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().
+
Example 1:
+ +Input: haystack = "hello", needle = "ll" +Output: 2 ++ +
Example 2:
+ +Input: haystack = "aaaaa", needle = "bba" +Output: -1 ++ +
+
Constraints:
+ +1 <= haystack.length, needle.length <= 104haystack and needle consist of only lowercase English characters.