I love this hat!! But, I am currently making this hat and am finding it off or too small! So, in response to "jexxican" the abbreviations are not typical. I figured out from the picture and from making the hat that:
"sc" is not a single crochet. it is a typical "hdc" half double crochet.
"hdc" is not a half double crochet, but a typical "dc" double crochet.
Hope that helps! Since I have tried it with those abbreviations, it worked out!!