题目描述
Problem Statement
You are given a sequence of length N: $A=(A_1,A_2,\ldots,A_N)$.
Find the number of triples (i,j,k) that satisfy both of the following conditions.
- $1\leq i \lt j \lt k \leq N$
- A_i, A_j, and A_k are distinct.
Input
Input is given from Standard Input in the following format:
N
$A_1 A_2 \ldots A_N$
Output
Print the answer.
Constraints
- $3 \leq N \leq 2\times 10^5$
- $1 \leq A_i \leq 2\times 10^5$
- All values in input are integers.
Sample Input 1
4
3 1 4 1
Sample Output 1
2
The two triples (i,j,k) satisfying the conditions are (1,2,3) and (1,3,4).
Sample Input 2
10
99999 99998 99997 99996 99995 99994 99993 99992 99991 99990
Sample Output 2
120
Sample Input 3
15
3 1 4 1 5 9 2 6 5 3 5 8 9 7 9
Sample Output 3
355
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分
样例输入
4
3 1 4 1
样例输出
2