.程序分析：可填在百位、十位、个位的数字都是1、2、3、4。组成所有的排列后再去 掉不满足条件的排列。(Program analysis: the number that can be filled in 100 bits, ten bits and bits is 1, 2, 3, 4. Make all the arrangements and then go An arrangement that is not satisfied.)