Kata

Given a sequence of integers of length n, print the number of prefix permutations within it.

A prefix permutation is an index P that satisfies :

• 0 <= P < N
• the sequence A[0], A[1], .....A[P] is a permutation of integers from 1 to P + 1

Example :

if given sequence is [2,1,3,5,4], then ...
  [2]         is NOT a permuation of [1]
  [2,1]       IS a permutation of [1,2]
  [2,1,3]     IS a permutation of [1,2,3]
  [2,1,3,5]   is NOT a permutation of [1,2,3,4]
  [2,1,3,5,4] IS a permutation of [1,2,3,4,5]

...and there are 3 prefix permutations