Hashi-o-kakero (21x21 hard)
Hashi-o-kakero (Bridges) is a logic puzzle game. The object is to connect all of the islands into a single connected group.
9 x 9 easy | 9 x 9 medium | 9 x 9 hard
11 x 11 easy | 11 x 11 medium | 11 x 11 hard
13 x 13 easy | 13 x 13 medium | 13 x 13 hard
17 x 17 easy | 17 x 17 medium | 17 x 17 hard
21 x 21 easy | 21 x 21 medium | 21 x 21 hard
How to play
The object of the game is to connect the islands by drawing a series of bridges between the islands. The number in the center of each island represents the number of bridges connected to it. The bridges must begin and end at distinct islands, traveling a straight line in between and not crossing any other bridges or islands. Only one or two bridges can connect a pair of islands. To build a bridge between two islands click on the first (it will appear as selected) then click to another. If you wish one more bridge between those two island repeat the procedure. If you make it again those two bridges will disappear.
Example
The beginning of the game will be only islands and no bridges connecting them It will look something similar to this image:
To solve the puzzle you have to connect all the islands taking into account the number in each island - this represents the exact number of bridges to reach it. Two neighboring island may not or can be joined together with one or two bridges. Bridges can not cross with each other. There can only be placed horizontally or vertically on the board. It is also important to know that each pair of islands must be connected either directly or to have some "indirect" connection.
Here's one way to solve the puzzle given above. "The easiest" here is an island that is located at the bottom left of the board. It can be associated only with the neighboring island to the right and have only one bridge. To join them we click on it:
After that we click on the island on the right and the bridge appears:
We continue in the same way building more bridges that are obvious:
On the next image we show how we have connected the topmost islands:
This is completely wrong, since this group of bridges will be "isolated" from others. But the rule say that between any 2 islands must have direct or indirect connection. So we have to remove those bridges. This can be done making another virtual island between the islands
And this is how it should be:
The island in the middle should have 5 bridge, but we are only 2 built. Since there are already 2 bridges and we cannot build another the only choice is to build those 3 remaining bridges between 2 horizontally neighboring islands. So we must have at least one bridge left and right.
Following similar thoughts come to this:
There are 2 remaining options - either to connect the island with "5" with the island with "4" and then the puzzle becomes trivial:
or connect two adjacent vertical islands with two bridges and hence to a different solution:
Not every puzzle can have multiple solutions. We choose exactly this to show you a wider range of possible hashi-o-kakero games.
Helpfull links
More information can be found on wikipedia site: Bridges_(puzzle).