How to Solve Count the Number of Computer Unlocking Permutations Problem

You are given an array complexity of length n. There are n locked computers in a room with labels from 0 to n - 1, each with its own unique password. The password of the computer i has a complexity complexity[i]. The password for the computer labeled 0 is already decrypted and serves as the root. All other computers must be unlocked using it or another previously unlocked computer, following this information: Find the number of permutations of [0, 1, 2, ..., (n - 1)] that represent a valid order in which the computers can be unlocked, starting from computer 0 as the only initially unlocked one. Since the answer may be large, return it modulo 109 + 7. Note that the password for the computer with label 0 is decrypted, and not the computer with the first position in the permutation.