2012 ToT Spring Junior A p6 find PIN number of Inspector Gadget
Source:
March 4, 2020
combinatorics
Problem Statement
A bank has one million clients, one of whom is Inspector Gadget. Each client has a unique PIN number consisting of six digits. Dr. Claw has a list of all the clients. He is able to break into the account of any client, choose any digits of the PIN number and copy them. The n digits he copies from different clients need not be in the same positions. He can break into the account of each client, but only once. What is the smallest value of which allows Dr.Claw to determine the complete PIN number of Inspector Gadget?