1990 USAMO 第 1 题

A certain state issues license plates consisting of six digits (from 0 through 9). The state requires that any two plates differ in at least two places. (Thus the plates $\boxed{027592}$ and $\boxed{020592}$ cannot both be used.) Determine, with proof, the maximum number of distinct license plates that the state can use.

某个州颁发由六位数字(从 0 到 9)组成的车牌。国家要求任意两块车牌至少有两处不同。 (因此车牌 $\boxed{027592}$ 和 $\boxed{020592}$ 不能同时使用。)通过证据确定该州可以使用的不同车牌的最大数量。