请问这道题用信息论怎样种思路来解呢？3X！

Suppose one has n balls, among which there may or may not be one counterfeit ball. If there is a counterfeit ball, it may be either heavier or lighter than the other balls. The balls are to be weighed by a balance.
(1) Find an upper bound on the number of balls n so that k weighings will find the counterfeit ball (if any) and correctly declare it to be heavier or lighter.

先求总的不确定量多少，然后求称一次减少的不确定量多少，做个除法就知道需要称几次了