Function parse

pub fn parse(input: &str) -> Input

Parse the input into an adjacency matrix of edges compressed into u32 bitfields.

First, each cave is assigned a unique index, with 0 reserved for the start cave and 1 reserved for the end cave. For example the sample input caves are:

start	end	A	b	c	d
0	1	2	3	4	5

Next a vec of u32 with an entry for each cave at the corresponding index is created with a bit set for each other cave reachable at 2^n where n is the cave index. The start cave can only be visited once at the beginning, so it is removed from all edges. For example the sample start cave vec looks like:

cave	index	edges
start	0	1100
end	1	1100
A	2	11010
b	3	100110
c	4	100
d	5	1000

Finally all small caves are added to a single u32, for example the sample data looks like 111011.