An online computer system for trading stock needs to process orders of the form"buy 100 shares at $x each" or "sell 100 shares at $y each. "A buy order for $x can only be processed if there is an existing sell order with price $y such that  y<=x. Likewise, a sell order for $y can only be processed if there is an existing buy order with price $x such that x>=y. If a buy or sell order is entered but cannot be processed, it must wait for a future order that allows it to be processed. Based on the above scenario, describe a scheme that allows for buy and sell orders to be entered in O(logn) time, independent of whether or not they can be immediately processed.