Almost Triple Deletions

2000ms

262144K

Description:

You are given an integer $$$n$$$ and an array $$$a_1,a_2,\ldots,a_n$$$.

In one operation, you can choose an index $$$i$$$ ($$$1 \le i \lt n$$$) for which $$$a_i \neq a_{i+1}$$$ and delete both $$$a_i$$$ and $$$a_{i+1}$$$ from the array. After deleting $$$a_i$$$ and $$$a_{i+1}$$$, the remaining parts of the array are concatenated.

For example, if $$$a=[1,4,3,3,6,2]$$$, then after performing an operation with $$$i=2$$$, the resulting array will be $$$[1,3,6,2]$$$.

What is the maximum possible length of an array of equal elements obtainable from $$$a$$$ by performing several (perhaps none) of the aforementioned operations?

Input:

Each test contains multiple test cases. The first line of input contains one integer $$$t$$$ ($$$1 \le t \le 1000$$$) — the number of test cases. The following lines contain the descriptions of the test cases.

The first line of each test case contains a single integer $$$n$$$ ($$$1 \le n \le 5000$$$) — the length of array $$$a$$$.

The second line of each test case contains $$$n$$$ integers $$$a_1,a_2,\ldots,a_n$$$ ($$$1 \le a_i \le n$$$) — the elements of array $$$a$$$.

It is guaranteed that the sum of $$$n$$$ across all test cases does not exceed $$$10\,000$$$.

Output:

For each testcase, print a single integer, the maximum possible length of an array of equal elements obtainable from $$$a$$$ by performing a sequence of operations.

Sample Input:

5
7
1 2 3 2 1 3 3
1
1
6
1 1 1 2 2 2
8
1 1 2 2 3 3 1 1
12
1 5 2 3 3 3 4 4 4 4 3 3

Sample Output:

Note:

For the first testcase, an optimal sequence of operations would be: $$$[1,2,3,2,1,3,3] \rightarrow [3,2,1,3,3] \rightarrow [3,3,3]$$$.

For the second testcase, all elements in the array are already equal.

For the third testcase, the only possible sequence of operations is: $$$[1,1,1,2,2,2] \rightarrow [1,1,2,2] \rightarrow [1,2] \rightarrow []$$$. Note that, according to the statement, the elements deleted at each step must be different.

For the fourth testcase, the optimal sequence of operations is: $$$[1,1,2,2,3,3,1,1] \rightarrow [1,1,2,3,1,1] \rightarrow [1,1,1,1]$$$.

For the fifth testcase, one possible reachable array of two equal elements is $$$[4,4]$$$.

Informação

Provedor Codeforces

Código CF1699D