The order of minimization is: 2,4,3, 1.

Only guess 4 is correct.

In other words, the first place is neither Class 3 guessed by Xiaoming, Class 2 guessed by Xiaohua, nor Class 4, because Class 4 is the second place, so the first place can only be 1 class.

By analogy, the third place is neither 1 class, nor class 3, nor class 4, but only class 2. The fourth place can only be Class 3.

So it is: 1, 4, 2, 3.