Implement strStr()

Implement strStr().

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

Update (2014-11-02):
The signature of the function had been updated to return the index instead of the pointer. If you still see your function signature returns a char *or String, please click the reload button  to reset your code definition.

public class Solution {
    public int strStr(String haystack, String needle) 
    {
        if(needle.length()==0)
        return 0;
        
        for (int i=0;i<haystack.length();i++)
        {
            if (haystack.length() - i +1 < needle.length())
            return -1;
            
            int j = 0;
            int k = i;
            
            while(j<needle.length()&&k<haystack.length()&&needle.charAt(j)==haystack.charAt(k))
            {
                j++;
                k++;
                if(j==needle.length())
                return i;
            }
            
        }
        
        return -1;
    }
}