Degree of Separation

The Introduction Problem

In genteel 18th/19th century British manners, it was extremely impolite to speak to someone without previously having been formally introduced. In order for two persons Algernon and Bunbury to be formally introduced, it required a third party Cecily -- who had already been introduced to both Algernon and Bunbury -- to introduce them to each other.

Given a set of people, two people X and Y out of that set who wish to speak to each other, and a list of pairs of people who are acquainted (i.e. have already been formally introduced), find the smallest set of people required to perform the (series of) introductions necessary to allow X and Y to speak to each other.

Write a program embodying your solution to the problem, which runs as follows:

<INPUT.TXT>

The first argument is a plain text file of acquaintance relationships in the format:

NAME:NAME NAME:NAME ...

The other two arguments are two names X and Y. The program should print the smallest number of other people required to perform the introductions in order for X and Y to be acquainted. (If X and Y are already acquainted, print 0.)

Sample input file: robert:cora kevin:billy cora:steve kevin:steve