Slitherlink is a type of logic puzzle made popular by Nikoli, the same Japanese puzzle company that has made Sudoku popular the world over. Like
most good logic puzzles, it has a set of very basic rules that can nonetheless result in devilishly difficult (and delightful!) puzzling experiences.
The rules of Slitherlink are as follows:
A Slitherlink board is made up of a lattice of dots; in this problem, it will be a regular rectangular lattice.
Some of the boxes (or cells) defined by the lattice have numbers within them; with a regular rectangular lattice, the numbers will be between 0
and 3 inclusive.
The goal of a Slitherlink puzzle is to connect adjacent dots (horizontally or vertically, like the sides of boxes) so that there is a single loop that
never crosses itself, with no line segments that are not part of the loop (no "dangling" segments or other, separate loops) such that every cell
that has a number has exactly that many sides as segments of the loop.
Given a supposedly solved Slitherlink puzzle, your task will be to determine whether or not it is indeed legitimately solved.