Unshuffle

A shuffle of two strings is formed by interspersing the characters into a new string, keeping the characters of each string in order. For example, MISSISSIPPI is a shuffle of MISIPP and SSISI. Let me call a string square if it is a shuffle of two identical strings. For example, ABCABDCD is square, because it is a shuffle of ABCD and ABCD, but the string ABCDDCBA is not square.
Given a square string, in which each character occurs no more than four times, unshuffle it into two identical strings.

First line, number of test cases, T.
Following are 2*T lines. For every two lines, the first line is n, length of the square string; the second line is the string. Each character is a positive integer no larger than n.

T<=10, n<=2000.

T lines. Each line is a string of length n of the corresponding test case. '0' means this character belongs to the first string, while '1' means this character belongs to the second string. If there are multiple answers, output any one of them.

1
8
1 2 3 1 2 4 3 4

00011011

2013 Multi-University Training Contest 6