Why the 0 Clue is Your Best Friend
The humble 0 might seem boring, but it is the most powerful starting clue in any Slitherlink puzzle.
The Power of Nothing
In a game about drawing lines, a number that tells you not to draw lines might seem unexciting. But the "0" clue is arguably the most powerful weapon in your arsenal. It doesn't just clear space; it forces the path of the loop into predictable channels.
Immediate Elimination
The first rule of 0 is simple: Eliminate all 4 edges around it immediately.
Mark them with Xs. This creates a "dead zone" where the loop cannot go. This absolute certainty is rare in logic puzzles. Unlike a "2" which has multiple configurations, a "0" has only one state: empty.
· · · × 0 × · × · × ·
The Cascade Effect
The real magic happens when a 0 is next to other numbers. Because the 0 blocks shared edges, it heavily constrains its neighbors:
- 0 next to 3: This is a classic forced move. A 3 needs 3 lines. If one side is blocked by a 0, the remaining 3 sides must be lines. You can fill them instantly.
· ·───· · ·
│ 3 × 0 ×
· ·───· × · × ·
Corner Power
A 0 in a corner is even stronger. It eliminates the two outer edges of the corner, effectively changing the shape of the grid. It also interacts with the diagonal neighbor in interesting ways. If you have a 0 in the corner and a 3 diagonally adjacent to it, that 3 becomes very constrained.
Strategy: Hunt the Zeros
When you start a new puzzle, your eyes should scan for 0s first. Process every single 0 before you look at anything else. Mark the Xs around them. Then check their neighbors. This "preprocessing" step often solves 10-20% of the board before you really start thinking.
Remember: 0s are rare in hard puzzles. When you see one, appreciate it. It's a gift from the puzzle setter.