28 Implement strStr().java

/*Leetcode 28. Implement strStr()
Implement strStr().
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.
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. This is consistent to C's strstr() and Java's indexOf().


Example 1:
Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:
Input: haystack = "aaaaa", needle = "bba"
Output: -1
 

Constraints:
1 <= haystack.length, needle.length <= 104
haystack and needle consist of only lowercase English characters.
*/


class Solution {
    public int strStr(String haystack, String needle) {
        if (needle.length() == 0){
            return 0;
        }
        
        for(int i = 0; i <= haystack.length() - needle.length(); i++){
            if(haystack.substring(i, i + needle.length()).equals(needle)){
                return i;
            }
        }
        return -1;
    }
}