243. Find the Index of the First Occurrence

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. An empty needle returns 0. Input: '"haystack", "needle"'.

Input: '"haystack", "needle"'.

Output: Integer — index or -1.

Examples

Input: "sadbutsad", "sad"
Output: 0
Explanation: First 'sad' at index 0.

Input: "leetcode", "leeto"
Output: -1
Explanation: Not present.

Input: "hello", "ll"
Output: 2
Explanation: 'll' at index 2.

Constraints

• 1<=haystack.length<=10^4
• 0<=needle.length<=10^4

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