link of the problem is : https://www.spoj.com/problems/TPGA/ https://www.spoj.com/problems/TPGA/

i am solving spoj problem in which i have to find the rank of the permutations when the integers lexicographically arranged means eg.

1 2 3 1 3 2 2 1 3 2 3 1 3 1 2 3 2 1

rank of 132 is 2. now i want to know how can i solve this using binary index tree ,i found this problem on coding portal in which this problem was queued under the Binary Index Problems someone help. give idea at least.