IMPC16 Group Contests |
Start: Jan.16.2016 at 10:00:00 AM
Finish: Jan.16.2016 at 02:00:00 PM
The contest is finished!
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Time limit 2000/4000/4000/4000 ms. Memory limit 65000/65000/65000/65000 Kb.
Sum of the Pairs
Your math professor is writing a list of unique
numbers and is asking you to give him the number of
pairs whose sum is equal to X. The professor is very
busy now and wants you to do the calculations quickly
and to give him the final result.
Question:
Given a list of n unique numbers, output the number
of pairs whose sum is equal to X.
Input specification:
In the first line you will be given two integers n and
X (5 <= n <= 200.000, -100.000 <= X <= 100.000), where
n determines the number of integers that the list will
contain and X determines the sum which the numbers of
each pair should give as their sum when added to each
other. In the following line, you will be given n
integers (-100.000 <= nr <= 100.000).
Output specification:
Write a single number, the number of pairs whose sum
is equal to X.
Sample Input I
5 7
1 2 3 4 5
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Sample Input II
10 7
4 6 3 1 7 5 11 -3 2 -1
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Sample Output I
2
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Sample Output II
3
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Explanation 1:
There are two pairs whose sum is equal to 7: (2,5) and (3,4).
Explanation 2:
There are three pairs whose sum is equal to 7: (4,3), (6,1) and (5,2)
Для отправки решений необходимо выполнить вход.
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