Implement strStr()

Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:

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

Example 2:

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

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().

on^2

class Solution {
    public int strStr(String haystack, String needle) {
        if(needle == null || 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;
    }
}