124. Implement strStr()

Easy · String

Implement the strStr() function to find the first occurrence of a needle string within a haystack string. Return the index of the first occurrence, or -1 if the needle is not found in the haystack.

This is a classic string matching problem. You may use built-in string search methods, or implement your own matching algorithm.

Examples

Example 1
Input: haystack = "hello", needle = "ll"
Output: 2
Explanation: "ll" first appears at index 2 in "hello".
Example 2
Input: haystack = "aaaa", needle = "bbb"
Output: -1
Explanation: "bbb" does not appear in "aaaa", so return -1.

Constraints