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LiveCodeBench / 1899_D / D. Yarik and Musical Notes
Problem
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contest date
2023-10-17T00:00:00
contest id
1899
difficulty
hard
platform
codeforces
question content
Yarik is a big fan of many kinds of music. But Yarik loves not only listening to music but also writing it. He likes electronic music most of all, so he has created his own system of music notes, which, in his opinion, is best for it.
Since Yarik also likes informatics, in his system notes are denoted by integers of , where — a positive integer. But, as you know, you can't use just notes to write music, so Yarik uses combinations of two notes. The combination of two notes , where and , he denotes by the integer .
For example, if , , then the combination is denoted by the integer . Note that different combinations can have the same notation, e.g., the combination is also denoted by the integer .
Yarik has already chosen notes that he wants to use in his new melody. However, since their integers can be very large, he has written them down as an array of length , then the note is . The integers in array can be repeated.
The melody will consist of several combinations of two notes. Yarik was wondering how many pairs of notes exist such that the combination is equal to the combination . In other words, he wants to count the number of pairs such that . Help him find the number of such pairs.
Input
The first line of the input contains one integer () — the number of test cases.
The first line of each test case contains one integer () — the length of the arrays.
The next line contains integers () — array .
It is guaranteed that the sum of over all test cases does not exceed .
Output
For each test case, output the number of pairs that satisfy the given condition.Sample Input 1:
5
1
2
4
3 1 3 2
2
1000 1000
3
1 1 1
19
2 4 1 6 2 8 5 4 2 10 5 10 8 7 4 3 2 6 10
Sample Output 1:
0
2
1
3
19
Plain-text mathematical notation (without MathML)
Yarik is a big fan of many kinds of music. But Yarik loves not only listening to music but also writing it. He likes electronic music most of all, so he has created his own system of music notes, which, in his opinion, is best for it. Since Yarik also likes informatics, in his system notes are denoted by integers of 2^(k), where k≥1 — a positive integer. But, as you know, you can't use just notes to write music, so Yarik uses combinations of two notes. The combination of two notes (a,b), where a=2^(k) and b=2^(l), he denotes by the integer a^(b). For example, if a=8=2³, b=4=2², then the combination (a,b) is denoted by the integer a^(b)=8⁴=4096. Note that different combinations can have the same notation, e.g., the combination (64,2) is also denoted by the integer 4096=64². Yarik has already chosen n notes that he wants to use in his new melody. However, since their integers can be very large, he has written them down as an array a of length n, then the note i is b_(i)=2^(a_(i)). The integers in array a can be repeated. The melody will consist of several combinations of two notes. Yarik was wondering how many pairs of notes b_(i),b_(j) (i<j) exist such that the combination (b_(i),b_(j)) is equal to the combination (b_(j),b_(i)). In other words, he wants to count the number of pairs (i,j) (i<j) such that b_(i)^(b_(j))=b_(j)^(b_(i)). Help him find the number of such pairs. Input The first line of the input contains one integer t (1≤t≤10⁴) — the number of test cases. The first line of each test case contains one integer n (1≤n≤2⋅10⁵) — the length of the arrays. The next line contains n integers a₁,a₂,…,a_(n) (1≤a_(i)≤10⁹) — array a. It is guaranteed that the sum of n over all test cases does not exceed 2⋅10⁵. Output For each test case, output the number of pairs that satisfy the given condition.Sample Input 1: 5 1 2 4 3 1 3 2 2 1000 1000 3 1 1 1 19 2 4 1 6 2 8 5 4 2 10 5 10 8 7 4 3 2 6 10 Sample Output 1: 0 2 1 3 19
Original LaTeX notation
Yarik is a big fan of many kinds of music. But Yarik loves not only listening to music but also writing it. He likes electronic music most of all, so he has created his own system of music notes, which, in his opinion, is best for it.
Since Yarik also likes informatics, in his system notes are denoted by integers of $2^k$, where $k \ge 1$ — a positive integer. But, as you know, you can't use just notes to write music, so Yarik uses combinations of two notes. The combination of two notes $(a, b)$, where $a = 2^k$ and $b = 2^l$, he denotes by the integer $a^b$.
For example, if $a = 8 = 2^3$, $b = 4 = 2^2$, then the combination $(a, b)$ is denoted by the integer $a^b = 8^4 = 4096$. Note that different combinations can have the same notation, e.g., the combination $(64, 2)$ is also denoted by the integer $4096 = 64^2$.
Yarik has already chosen $n$ notes that he wants to use in his new melody. However, since their integers can be very large, he has written them down as an array $a$ of length $n$, then the note $i$ is $b_i = 2^{a_i}$. The integers in array $a$ can be repeated.
The melody will consist of several combinations of two notes. Yarik was wondering how many pairs of notes $b_i, b_j$ $(i < j)$ exist such that the combination $(b_i, b_j)$ is equal to the combination $(b_j, b_i)$. In other words, he wants to count the number of pairs $(i, j)$ $(i < j)$ such that $b_i^{b_j} = b_j^{b_i}$. Help him find the number of such pairs.
Input
The first line of the input contains one integer $t$ ($1 \le t \le 10^4$) — the number of test cases.
The first line of each test case contains one integer $n$ ($1 \leq n \leq 2 \cdot 10^5$) — the length of the arrays.
The next line contains $n$ integers $a_1, a_2, \dots, a_n$ ($1 \leq a_i \leq 10^9$) — array $a$.
It is guaranteed that the sum of $n$ over all test cases does not exceed $2 \cdot 10^5$.
Output
For each test case, output the number of pairs that satisfy the given condition.Sample Input 1:
5
1
2
4
3 1 3 2
2
1000 1000
3
1 1 1
19
2 4 1 6 2 8 5 4 2 10 5 10 8 7 4 3 2 6 10
Sample Output 1:
0
2
1
3
19
question title
D. Yarik and Musical Notes
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