Random image from array

The following code works but I would like it to be modified so that the same image never shows twice.

var pics:Array = new Array();
pics[0] = “text/theatre1.jpg”;
pics[1] = “text/theatre2.jpg”;
pics[2] = “text/theatre3.jpg”;
pics[3] = “text/theatre4.jpg”;
function showRandomPic() {
var n:Number = Math.ceil(Math.random()*pics.length-1); //create random number
pic_mc.loadMovie(pics[n]); // load associated image from random number

Could somebody please modifiy this and repost it so that it won’t chose the same pic twice.

Thanks in advance