Implement strStr()

basically, we need to implement indexOf()

so this problem is actually a string matching problem.
we met many of such string pattern matching algorithm.

a very simple one, but you did a pretty shit job as always.

class Solution {
    public int strStr(String haystack, String needle) {
        if (needle == null || needle.length() == 0) return 0; //the most connered case should be in the first place, and it matters
        if (haystack == null || haystack.length() == 0) return -1;
        
        if (haystack.length() < needle.length()) return -1;
        
        
        int i = 0;
        int j = 0;
        
        while (i < haystack.length()) {
            int start = i;
            while (i < haystack.length() && j < needle.length() && haystack.charAt(i) == needle.charAt(j)) {
                if (j == needle.length() - 1) {
                    return i - needle.length() + 1;
                }
                
                i++;
                j++;
                
            }
            i = start + 1;
            j = 0;
        }
        return -1;
    }
}