#P1637. Counting Thair Subsequences
Counting Thair Subsequences
Counting Thair Subsequences
Erwin is fascinated by a concept called thair
. In a sequence of n integers, thair
is defined as a triple of numbers ai, aj, ak such that i < j < k and ai < aj < ak. In other words, three numbers form a thair
if and only if:
$i<j<k$ and $a_i<a_j<a_k$
Your task is to count the number of thair
triples in the given sequence.
inputFormat
The input consists of two lines. The first line contains an integer n ($1 \leq n \leq 10^5$ depending on constraints). The second line contains n space-separated integers representing the sequence: a1, a2, ..., an.
outputFormat
Output a single integer, which is the number of thair
triples in the given sequence.
sample
3
1 2 3
1
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