三元逆序对 求i<j<k && a[i]>a[j]>a[k] 的对数 树状数组Codeforces 61E Enemy is weak

http://codeforces.com/problemset/problem/61/E

E. Enemy is weak

time limit per test

5 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

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