CF61E.Enemy is weak
普及/提高-
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题目描述
The Romans have attacked again. This time they are much more than the Persians but Shapur is ready to defeat them. He says: "A lion is never afraid of a hundred sheep".
Nevertheless Shapur has to find weaknesses in the Roman army to defeat them. So he gives the army a weakness number.
In Shapur's opinion the weakness of an army is equal to the number of triplets i,j,k such that i<j<k and a_{i}>a_{j}>a_{k} where ax is the power of man standing at position x . The Roman army has one special trait — powers of all the people in it are distinct.
Help Shapur find out how weak the Romans are.
罗马人再次发动进攻。这次他们比波斯人强大得多,但沙普尔已经做好了打败他们的准备。他说:"一头狮子永远不怕一百只绵羊"。
然而,沙普尔必须找到罗马军队的弱点才能打败他们。于是,他给军队编了一个弱点号码。
沙普尔认为,一支军队的弱点等于 i < j < k 和 ai > aj > ak 的三联数 i, j, k ,其中 ax 是站在 x 位置上的人的力量。罗马军队有一个特点--军队中所有人的力量都是不同的。
帮助沙普尔找出罗马人的弱点。
输入格式
The first line of input contains a single number n ( 3<=n<=106 ) — the number of men in Roman army. Next line contains n different positive integers ai ( 1<=i<=n,1<=ai<=109 ) — powers of men in the Roman army.
输入
第一行包含一个数字 n ( 3<=n<=106 ) - 罗马军队的人数。下一行包含 n 不同的正整数 ai ( 1<=i<=n,1<=ai<=109 ) - 罗马军队人数的幂
输出格式
A single integer number, the weakness of the Roman army.
Please, do not use %lld specificator to read or write 64-bit integers in C++. It is preffered to use cout (also you may use %I64d).
输出
一个整数,即罗马军队的弱点。
请不要使用 %lld specificator 在 C++ 中读写 64 位整数。最好使用 cout(也可以使用 %I64d)。
输入输出样例
输入#1
3 3 2 1
输出#1
1
输入#2
3 2 3 1
输出#2
0
输入#3
4 10 8 3 1
输出#3
4
输入#4
4 1 5 4 3
输出#4
1