-- your code goes here
local ballImages =
{
"ball1.png",
"ball2.png",
"ball3.png",
"ball4.png",
"ball5.png",
"ball6.png",
"ball7.png",
"ball8.png",
"ball9.png",
"ball10.png",
"ball11.png",
"ball12.png",
"ball13.png",
"ball14.png",
"ball15.png",
"ball16.png",
"ball17.png",
"ball18.png",
"ball19.png",
"ball20.png"
}

drawn = {}
local drop=4                                -- how many balls to draw
while drop > 0 do                           -- while we have balls left to draw
    local ball = math.random(#ballImages)   -- draw a random ball

    if drawn[ball] == nil then              -- if ball wasn't selected before
        drawn[ball] = 1                     -- mark it as selected
        print(ballImages[ball])             -- "drop" the ball
        drop = drop - 1                     -- decrement how many more balls
    end 
end