What is Nonocross?
Nonocross is a picture logic puzzle - the same family of puzzle known around the world as a nonogram, and also called Picross (Nintendo), Griddler (UK), Hanjie (Japan), or "paint by numbers." You are given a blank rectangular grid with a set of number clues along the top (for each column) and down the left side (for each row). By working out which cells are filled and which are empty, you gradually reveal a hidden picture - a crab, a heart, a tortoise, and so on.
The best part: a well-made Nonocross puzzle has exactly one solution, and you never have to guess. Every filled cell can be worked out through pure logic from the clues you're given.
The Goal
Fill in the correct cells so that:
- Every row matches its number clues, and
- Every column matches its number clues at the same time.
When both are satisfied for the whole grid, the puzzle is solved and the picture appears.
How the Number Clues Work
This is the single most important rule to understand:
- Each number tells you how many consecutive filled cells appear in that line (row or column).
- A clue with several numbers means several separate groups of filled cells, shown in order - left to right for rows, top to bottom for columns.
- There must be at least one empty cell between two groups.
- A clue of 0 means the entire line is empty.
■■■▪▪■▪▪.
The clue tells you the sizes and the order, but not yet the exact positions - that's what you deduce.
A Worked Example (5×5 Cross)
Here is a small solved Nonocross. Read a filled square (indigo) as "filled" and an × as "empty." Notice how each row and column exactly matches its clue numbers:
| 1 | 1 | 5 | 1 | 1 | |
| 1 | |||||
| 1 | |||||
| 5 | |||||
| 1 | |||||
| 1 |
Column clues on top (1, 1, 5, 1, 1) and row clues on the left (1, 1, 5, 1, 1) both check out - the filled cells form a cross (a fitting shape for Nonocross).
Filling vs. Marking Empty
Good solvers track two things, not one. As you deduce cells:
- Fill the cells you know are part of a group.
- Mark an × on cells you know are empty.
Marking empties is just as valuable as filling - an × in a row often tells you exactly where a group in a column must start or end. In most Nonocross apps you tap/left-click to fill and long-press/right-click to mark an ×.
Step-by-Step: How to Solve a Puzzle
- Scan for the easy lines first. A clue of 0 means the whole line is empty - mark every cell with an ×. A clue equal to the line's full length (e.g. 5 on a 5-cell row) means the whole line is filled.
- Attack the biggest clues with the overlap method (explained below) to lock in guaranteed cells.
- Mark the empties you can prove, to squeeze the remaining unknowns.
- Cross-reference: switch between rows and columns constantly. Each cell you solve in a row is new information for its column, and vice versa.
- Repeat until every cell is decided. The hidden picture is your confirmation.
Core Solving Strategies
1. The Overlap Method (the #1 technique)
For a large clue, slide the group as far left as it can go, then as far right as it can go. Any cell that is filled in both positions must be filled in the solution.
2. Edge Logic
If you know the first cell of a line is filled, then the first clue group must start exactly there, so you can fill its whole length immediately. The same works from the far end with the last group. Edges are the easiest place to get a foothold.
3. Full-Line Completion
Add up all the clue numbers plus the minimum one-cell gaps between groups. If that total equals the line's length, there is only one arrangement - fill it in completely. For example, clue 2 1 2 on an 8-cell row needs 2 + 1 + 1 + 1 + 2 = 7... with one cell of slack, so it's almost forced; clue 2 2 2 on an 8-cell row needs exactly 8 and is fully forced.
4. Gap Analysis
Look at a run of unknown cells bounded by × marks or grid edges. If that gap is smaller than the smallest remaining group, no group can fit - mark the whole gap empty. This quickly eliminates dead space.
5. Cross-Referencing (Rows ↔ Columns)
This is what makes nonograms solvable without guessing. A single cell you prove filled or empty in a row feeds straight into its column's logic. Keep bouncing back and forth - progress in one direction almost always unlocks the other.
Common Mistakes to Avoid
- Forgetting the mandatory gap. Groups in the same line must have at least one empty cell between them.
- Ignoring the × marks. Empty cells carry as much information as filled ones - track them.
- Guessing. One wrong fill cascades into a broken picture. Every move should be provable.
- Tunnel vision on rows. If a row stalls, jump to the columns crossing it.
Frequently Asked Questions
Do I ever need to guess in Nonocross?
No. A properly designed puzzle has a single solution reachable by logic alone. If you're stuck, look harder for a forced cell.
What does a clue of 0 mean?
The entire row or column is empty - mark every cell in it with an ×.
What if a row has no numbers or just one big number?
A single number equal to the line length fills the whole line. A single small number is where the overlap method shines.
Is Nonocross the same as Picross or nonograms?
Yes - they're the same puzzle type under different names. Any nonogram/Picross technique works in Nonocross.