问题1354--Xenia and Divisors

1354: Xenia and Divisors

时间限制: 1 Sec  内存限制: 256 MB
提交: 97  解决: 38
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题目描述
Xenia the mathematician has a sequence consisting of n (n is divisible by 3) positive integers, each of them is at most 7. She wants to split the sequence into groups of three so that for each group of three a,b,c the following conditions held:
·       a<b<c;
·       a divides b, b divides c.
Naturally, Xenia wants each element of the sequence to belong to exactly one group of three. Thus, if the required partition exists, then it has  groups of three.
Help Xenia, find the required partition or else say that it doesn't exist.
输入
The first line contains integer n (3n99999) — the number of elements in the sequence. The next line contains n positive integers, each of them is at most 7.
It is guaranteed that n is divisible by 3.
输出
If the required partition exists, print  groups of three. Print each group as values of the elements it contains. You should print values in increasing order. Separate the groups and integers in groups by whitespaces.(按照非递增顺序输出)
If there is no solution, print -1.
样例输入 Copy
6
1 1 1 2 2 2
6
2 2 1 1 4 6
样例输出 Copy
-1
1 2 4
1 2 6
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