Problem 42494. Which permutation is it?

Let write some permutations of positive integers.

    1:    1 2 3 4 5 6 ...
    2:    2 1 3 4 ...
    3:    1 3 2 4 ...
    4:    2 3 1 4 ...
    5:    3 1 2 4 ...
    6:    3 2 1 4 ...
   25:    1 2 3 5 4 ...
  120:    5 4 3 2 1 6 7 ...

Given a permutation of integers in range 1:n, return it's index following above pattern.

See also: 42495

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65.75% Correct | 34.25% Incorrect
Last Solution submitted on Dec 18, 2025

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