Sherlock and Inversions

4.8

13 votes
Algorithms, Approved, Hard, Open, Sqrt-Decomposition
Problem

Watson gives to Sherlock an array of N integers denoted by A1, A2 ... AN.
Now he gives him Q queries of form Li, Ri. For each such query Sherlock has to report the number of inversions in subarray denoted by [Li, Ri].

Inversions in a subarray denoted by [a, b] are number of pairs (i, j) such that ai < jb and Ai > Aj.

Input
First line contains N and Q. Next line contains N space separated integers denoting array A.
Each of the next Q lines contain two space separated integers denoting Li, Ri.

Output
For each query, print the required answer in one line.

Constraints
20% files: 1 ≤ N, Q ≤ 103
20% files: 1 ≤ N ≤ 103 and 1 ≤ Q ≤ 105
60% files: 1 ≤ N, Q ≤ 105
1 ≤ Ai ≤ 109
1 ≤ LiRiN

Time Limit: 5
Memory Limit: 256
Source Limit:
Explanation

query1: Number of inversions in B = [1, 4] is 0.

query2: Number of inversions in B = [2, 3, 1] are 2 since B[0]>B[2] and B[1]>B[2].

query3: Number of inversions in original array are 5.

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