Time Limit: 1000MS Memory Limit: 10000K Total Submissions: 39035 Accepted: 15135


One measure of unsortedness in a sequence is the number of pairs of entries that are out of order with respect to each other. For instance, in the letter sequence DAABEC, this measure is 5, since D is greater than four letters to its right and E is greater than one letter to its right. This measure is called the number of inversions in the sequence. The sequence AACEDGG has only one inversion (E and D)—it is nearly sorted—while the sequence ZWQM has 6 inversions (it is as unsorted as can be—exactly the reverse of sorted).

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