Given an array perm of length n which is a permutation of [1, 2, ..., n], return the index of perm in the lexicographically sorted array of all of the permutations of [1, 2, ..., n].
Since the answer may be very large, return it modulo 109 + 7.
Example 1:
Input: perm = [1,2]
Output: 0
Explanation:
There are only two permutations in the following order:
[1,2], [2,1]
And [1,2] is at index 0.
Example 2:
Input: perm = [3,1,2]
Output: 4
Explanation:
There are only six permutations in the following order:
[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], [3,2,1]
And [3,1,2] is at index 4.
Constraints:
1 <= n == perm.length <= 105perm is a permutation of [1, 2, ..., n].Loading editor...
[1,2]