Programmer Think

Record $l_{x} $is the guard path length passing through $x $. If there is no such guard, $l will be defined_ {x}=1$ Note that if you can get to $x $at time $t $, you can obviously get there at time $t+l_{x} $reaches $x $(follow the direction of the guard), so define $d_{x,s} $is the earliest time to reach $x $and $\ equiv s (MOD \ L {x}) $, tha ...