One-way flight trip problem

Question

You are going on a one-way indirect flight trip that includes billions an unknown very large number of transfers.

• You are not stoppi

Answer 1

Put in two Hashes: to_end = src -> des; to_beg = des -> src

Pick any airport as a starting point S.

while(to_end[S] != null)
   S = to_end[S];

S is now your final destination. Repeat with the other map to find your starting point.

Without properly checking, this feels O(N), provided you have a decent Hash table implementation.