#P1698D. Fixed Point Guessing

    ID: 7757 Type: RemoteJudge 1000ms 256MiB Tried: 0 Accepted: 0 Difficulty: (None) Uploaded By: Tags>binary searchconstructive algorithmsinteractive*1600

Fixed Point Guessing

No submission language available for this problem.

Description

This is an interactive problem.

Initially, there is an array a=[1,2,,n]a = [1, 2, \ldots, n], where nn is an odd positive integer. The jury has selected n12\frac{n-1}{2} disjoint pairs of elements, and then the elements in those pairs are swapped. For example, if a=[1,2,3,4,5]a=[1,2,3,4,5], and the pairs 141 \leftrightarrow 4 and 353 \leftrightarrow 5 are swapped, then the resulting array is [4,2,5,1,3][4, 2, 5, 1, 3].

As a result of these swaps, exactly one element will not change position. You need to find this element.

To do this, you can ask several queries. In each query, you can pick two integers ll and rr (1lrn1 \leq l \leq r \leq n). In return, you will be given the elements of the subarray [al,al+1,,ar][a_l, a_{l + 1}, \dots, a_r] sorted in increasing order.

Find the element which did not change position. You can make at most 15\mathbf{15} queries.

The array aa is fixed before the interaction and does not change after your queries.

Recall that an array bb is a subarray of the array aa if bb can be obtained from aa by deletion of several (possibly, zero or all) elements from the beginning and several (possibly, zero or all) elements from the end.

Each test contains multiple test cases. The first line contains an integer tt (1t5001 \leq t \leq 500) — the number of test cases. The description of the test cases follows.

The first line of each test case contains an integer nn (3n<1043 \leq n < 10^4; nn is odd) — the length of the array aa.

After reading the first line of each test case, you should begin the interaction.

It is guaranteed that the sum of nn over all test cases does not exceed 10410^4.

Interaction

For each test case, begin the interaction by reading the integer nn.

To make a query, output "?  l  r\texttt{?}\;l\;r" (1lrn1 \leq l \leq r \leq n) without quotes. Afterwards, you should read in rl+1r-l+1 integers — the integers al,al+1,,ara_l, a_{l + 1}, \dots, a_r, in increasing order. You can make at most 1515 such queries in a single test case.

If you receive the integer 1-1 instead of an answer or the integer nn, it means your program has made an invalid query, has exceed the limit of queries, or has given incorrect answer on the previous test case. Your program must terminate immediately to receive a Wrong Answer verdict. Otherwise you can get an arbitrary verdict because your solution will continue to read from a closed stream.

When you are ready to give the final answer, output "!  x\texttt{!}\;x" (1xn1 \leq x \leq n) without quotes — the element that did not change position. Giving this answer does not count towards the limit of 1515 queries. Afterwards, your program must continue to solve the remaining test cases, or exit if all test cases have been solved.

After printing a query do not forget to output end of line and flush the output. Otherwise, you will get Idleness limit exceeded. To do this, use:

  • fflush(stdout) or cout.flush() in C++;
  • System.out.flush() in Java;
  • flush(output) in Pascal;
  • stdout.flush() in Python;
  • see documentation for other languages.

Hacks

To make a hack, use the following format. The first line must contain an integer tt (1t5001 \leq t \leq 500) — the number of test cases. The description of the test cases follows.

The first line of each test case must contain an integer nn (3n<1043 \leq n < 10^4; nn is odd) — the length of the array aa.

The second line of each test case must contain nn space-separated integers a1,a2,,ana_1, a_2, \ldots, a_n (1ain1 \le a_i \le n) — the elements of aa. The array aa should be the result of n12\frac{n-1}{2} disjoint swaps on the array [1,2,,n][1,2,\dots,n].

Input

Each test contains multiple test cases. The first line contains an integer tt (1t5001 \leq t \leq 500) — the number of test cases. The description of the test cases follows.

The first line of each test case contains an integer nn (3n<1043 \leq n < 10^4; nn is odd) — the length of the array aa.

After reading the first line of each test case, you should begin the interaction.

It is guaranteed that the sum of nn over all test cases does not exceed 10410^4.

Samples

Sample Input 1

2
5

1 2 4 5

1 3 5

3

1

Sample Output 1

? 1 4

? 3 5

! 2

? 1 1

! 1

Note

In the first test, the interaction proceeds as follows.

SolutionJuryExplanation
2\texttt{2}There are 2 test cases.
5\texttt{5}In the first test case, the hidden array is [4,2,5,1,3][4,2,5,1,3], with length 55.
? 1 4\texttt{? 1 4}1 2 4 5\texttt{1 2 4 5}The solution requests the subarray [4,2,5,1][4,2,5,1] in increasing order, and the jury responds with [1,2,4,5][1,2,4,5].
? 3 5\texttt{? 3 5}1 3 5\texttt{1 3 5}The solution requests the subarray [5,1,3][5,1,3] in increasing order, and the jury responds with [1,3,5][1,3,5].
! 2\texttt{! 2}The solution has somehow determined that a2=2a_2=2, and outputs it. Since the output is correct, the jury continues to the next test case.
3\texttt{3}In the second test case, the hidden array is [1,3,2][1,3,2], with length 33.
? 1 1\texttt{? 1 1}1\texttt{1}The solution requests the number [1][1] only, and the jury responds with [1][1].
! 1\texttt{! 1}The solution has determined that a1=1a_1=1, and outputs it. Since the output is correct and there are no more test cases, the jury and the solution exit.

Note that the line breaks in the example input and output are for the sake of clarity, and do not occur in the real interaction.