The chords are:
F# (bar it or just play it on the first 3 strings)
D
A
E


CHORUS:
F#              D              A
Shawty's like a melody in my head
                  E
That I can't keep out
Got me singin' like
F#           D
Na na na na everyday
              A             E
It's like my iPod stuck on replay

F#                  D
Remember the first time we met
        A                  E
You was at the mall wit yo friend
I was scared to approach ya
But then you came closer
Hopin' you would give me a chance

Who would have ever knew
That we would ever be more than friends
We're real worldwide, breakin all the rules
She like a song played again and again

That girl, like somethin off a poster
That girl, is a dime they say
That girl, is a gun to my holster
She's runnin through my mind all day, ay

Chorus X2  and the rest of the song
just keep playing those 4 chords.