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.

Example 1:

• Input: haystack = “sadbutsad”, needle = “sad”
• Output: 0
• Explanation: “sad” occurs at index 0 and 6. The first occurrence is at index 0, so we return 0.

Example 2:

• Input: haystack = “leetcode”, needle = “leeto”
• Output: -1
• Explanation: “leeto” did not occur in “leetcode”, so we return -1.

Constraints:

• 1 <= haystack.length, needle.length <= 104
• haystack and needle consist of only lowercase English character- s.