Number Link was invented in 1932 by Henry Ernest Dudeney; Sam Lloyd had invented a previous version in 1897.
Puzzle and Goal
An unsolved puzzle consists of a rectangular grid. Some of the squares contain numbers (or letters).
The goal is to draw paths through orthogonally neighboring cells connecting pairs of numbers (or letters).
The solved grid must satisfy the following conditions:
All cells must contain part of a path.
No two paths can go through the same cell.
All clues must be on an end of a path; the other end must be the same number or letter.