Implement Strstr
Implement strstr(). Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. Example 1 Input: haystack = "hello", needle = "ll" Output: 2 Example 2 Input: haystack = "aaaaa", needle = "bba" Output: -1 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.