MathDB
Antitours in Mahishmati

Source: India TST 2023 Day 1 P1

July 9, 2023
combinatoricsgraph theory

Problem Statement

In the fictional country of Mahishmati, there are 5050 cities, including a capital city. Some pairs of cities are connected by two-way flights. Given a city AA, an ordered list of cities C1,,C50C_1,\ldots, C_{50} is called an antitour from AA if
[*] every city (including AA) appears in the list exactly once, and [*] for each k{1,2,,50}k\in \{1,2,\ldots, 50\}, it is impossible to go from AA to CkC_k by a sequence of exactly kk (not necessarily distinct) flights.
Baahubali notices that there is an antitour from AA for any city AA. Further, he can take a sequence of flights, starting from the capital and passing through each city exactly once. Find the least possible total number of antitours from the capital city.
Proposed by Sutanay Bhattacharya