find_the_index_of_the_first_occurence_in_a_string.go

/*
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 characters.
*/

package main

func strStr(haystack string, needle string) int {
	if haystack == "" || needle == "" {
			return -1;
	}
	if haystack == needle {
			return 0;
	}
	needleLength := len(needle);
	for i := 0; i < len(haystack) - needleLength + 1; i++ {
			if haystack[i:i + needleLength] == needle {
					return i;
			}
	}
	return -1;
}