CF1896A.Jagged Swaps

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题目描述

You are given a permutation ^\dagger aa of size nn . You can do the following operation

  • Select an index ii from 22 to n1n - 1 such that ai1<aia_{i - 1} < a_i and ai>ai+1a_i > a_{i+1} . Swap aia_i and ai+1a_{i+1} .

Determine whether it is possible to sort the permutation after a finite number of operations.

^\dagger A permutation is an array consisting of nn distinct integers from 11 to nn in arbitrary order. For example, [2,3,1,5,4][2,3,1,5,4] is a permutation, but [1,2,2][1,2,2] is not a permutation ( 22 appears twice in the array) and [1,3,4][1,3,4] is also not a permutation ( n=3n=3 but there is 44 in the array).

输入格式

Each test contains multiple test cases. The first line contains the number of test cases tt ( 1t50001 \le t \le 5000 ). Description of the test cases follows.

The first line of each test case contains a single integer nn ( 3n103 \le n \le 10 ) — the size of the permutation.

The second line of each test case contains nn integers a1,a2,,ana_1, a_2, \ldots, a_n ( 1ain1 \le a_i \le n ) — the elements of permutation aa .

输出格式

For each test case, print "YES" if it is possible to sort the permutation, and "NO" otherwise.

You may print each letter in any case (for example, "YES", "Yes", "yes", "yEs" will all be recognized as positive answer).

输入输出样例

  • 输入#1

    6
    3
    1 2 3
    5
    1 3 2 5 4
    5
    5 4 3 2 1
    3
    3 1 2
    4
    2 3 1 4
    5
    5 1 2 3 4

    输出#1

    YES
    YES
    NO
    NO
    NO
    NO

说明/提示

In the first test case, the permutation is already sorted.

In the second test case, we can choose index i=2i=2 as 1<31<3 and 3>23>2 to form [1,2,3,5,4][1, 2, 3, 5, 4] . Then, we can choose index i=4i=4 as 3<53<5 and 5>45>4 to form [1,2,3,4,5][1, 2, 3, 4, 5] .

In the third test case, it can be proven that it is impossible to sort the permutation.

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