# List of Coral variants

There are a lot of Coral variants. Refer to Coral for the standard definition of the word "coral" in here.

### First Seen Coral[edit]

First appeared on Moscow Cup 2009. The puzzle was written by Andrey Bogdanov (Russia).

Shade some cells so that all shaded cells are connected, all unshaded cells are connected to the border of the grid and no 2×2 square is completely shaded.

The clues outside the grids represent the length of the first filled cell block in that direction.

(Rules (modified) and example from WPC 2011 IB)

### Coral Snake[edit]

Hybrid with Snake. Invented by Rainer Biegler (Germany). First appeared on LMD portal in 2012.

Shade some cells to create a standard Coral and a standard Snake. Cells marked with circles contain the head and tail of the snake. Snake and coral cannot overlap, and coral cells and snake cells cannot share an edge, but they can touch diagonally.

The clues outside the grid describe the contents of the respective row or column. For each row or column, one of the numbers indicates the number of snake cells in the respective row or column; each other number corresponds to a contiguous group of coral cells, the number indicates the length of that group. However, if a row or column contains no coral cells or no snake cells at all, clue number 0 will be omitted.

(Rules (modified) and example from WPC 2019 IB)

### Coral Magnets[edit]

### Coral + Star Battle[edit]

Hybrid with Gaps rather than Star Battle. First appeared on LMD portal in 2015. Invented by Christian Halberstadt (Germany).

Shade some cells so that all shaded cells are connected, all unshaded cells are connected to the border of the grid and no 2×2 square is completely shaded.

Further, place stars into some unshaded cells, so that there are exactly two stars in each row and column. The stars do not touch each other, not even diagonally.

The clues outside the grid describe the contents of the respective row or column. For each row or column, one of the numbers indicates the number of cells between the two stars; each other number corresponds to a contiguous group of shaded cells, the number indicates the length of that group. Some numbers have been replaced by question marks. For each row and column, the clue numbers are sorted in increasing order, with the question marks always at the beginning, regardless of which numbers they replace. For some rows or columns, the clues have been omitted entirely.

(Rules from WPC 2019 IB)

### Tripod Coral[edit]

The "Tripod" rule is a common theme for region division puzzles, notably present in Tripod Sudoku. This variant first appeared in WPC 2016/Round 11. The puzzle was written by Matej Uher (Slovakia).

Shade some cells so that all shaded cells are connected, all unshaded cells are connected to the border of the grid and no 2×2 square is completely shaded. Numbers outside the grid indicate the lengths of all blocks of shaded cells in the corresponding row or column, not necessarily in the given order. Each cell that has exactly three shaded orthogonally adjacent cells is marked with a circle.

(Rules and example from WPC 2016 IB)

### Sky Coral[edit]

Hybrid with Skyscrapers clues. First appeared on WPC 2018/Round 3. The puzzle was written by Jiří Hrdina (Czech Rep.).

Shade some cells so that all shaded cells are connected, all unshaded cells are connected to the border of the grid and no 2×2 square is completely shaded.

The numbers at the borders indicate how many blocks are visible if the lengths of the blocks were their heights.

(Example from WPC 2018 IB)

### Coral with Vertex Hints[edit]

Similar additional rule to Tetroscope. First appeared on WPC 2018/Round 5. The puzzle was written by Jiří Hrdina.

The numbers on the vertices indicate the number of painted cells touching the given vertex.

(Example from WPC 2018 IB)

### Inner Coral[edit]

First appeared on WPC 2018/Round 5. The puzzle was written by Jiří Hrdina.

Shade some cells so that all shaded cells are connected, all unshaded cells are connected to the border of the grid and no 2×2 square is completely shaded. Clues denote **all** of the lengths of the first Coral segments visible from this cell in the four directions (vertically and horizontally) in no particular order.

(Example from WPC 2018 IB)

### Double Coral[edit]

First appeared on WPC 2018/Round 10, "Double Trouble". The puzzle was written by Jiří Hrdina.

Place two corals in the grid. Use X and O to mark the fields occupied by the two corals.

The numbers on the edge indicate the lengths of successive blocks of coral cells, but not necessarily in the correct order. There must be at least one other cell between two blocks. All the cells must be filled by at least one of the corals. All the cells where the corals overlap are marked. Hints on the right belong to one of the corals, hints below belong to the other one.

(Rules and Example from WPC 2018 IB)

### Regional Coral[edit]

First appeared on WPC 2018/Round 11, "Regional". The puzzle was written by Jiří Hrdina.

In each region, the exact same number of cells are shaded. Solvers must determine the number of shaded cells.

(Example from WPC 2018 IB)

### Coral with Letters[edit]

First appeared on WPC 2018/Round 12, "Innovatives". Invented by Jiří Hrdina.

Furthermore, place a given set of letters in the shaded cells so that each letter appears exactly once in each row and column. The clues around the grid show all the letters that can be found on the first coral segment from the given side, in the correct order (from top to bottom resp. from left to right). A dash means there is no letter on the first segment.

(Rules and example (A, B) from WPC 2018 IB)

## Appearances in the past WPCs[edit]

- WPC 2019/Round 2 (Coral Snake) by Rainer Biegler
- WPC 2019/Round 4 (First Seen Coral) by Roland Voigt
- WPC 2019/Team Playoffs (Coral + Star Battle) by Christian Halberstadt
- WPC 2018/Round 3 (Sky Coral) by Jiři Hrdina
- WPC 2018/Round 5 (Coral with Vertex Hints, Inner Coral) by Jiři Hrdina
- WPC 2018/Round 10 (Double Coral) by Jiři Hrdina
- WPC 2018/Round 11 (Regional Coral) by Jiři Hrdina
- WPC 2018/Round 12 (Coral with Letters) by Jiři Hrdina
- WPC 2018/Individual Playoffs (Double Coral, unused) by Jiři Hrdina
- WPC 2016/Round 11 (Tripod Coral) by Matej Uher
- WPC 2015/Round 5 (Coral Magnets)
- WPC 2015/Round 10 (Coral Maximum, Dotted Coral)
- WPC 2011/Part 13 (First Seen Coral)