Question

A derangement is a permutation of the elements such that none appear in its original position. For example, the only derangements of {1,2,3} are {2,3,1} and {3,1,2}

Answer 1

Answer:

Input: n = 2

Output: 1

For two elements say {0, 1}, there is only one

possible derangement {1, 0}

Input: n = 3

Output: 2

For three elements say {0, 1, 2}, there are two

possible derangements {2, 0, 1} and {1, 2, 0}

Input: n = 4

Output: 9

For four elements say {0, 1, 2, 3}, there are 9

possible derangements {1, 0, 3, 2} {1, 2, 3, 0}

{1, 3, 0, 2}, {2, 3, 0, 1}, {2, 0, 3, 1}, {2, 3,

1, 0}, {3, 0, 1, 2}, {3, 2, 0, 1} and {3,

Hope this will help you