Rules: Shade some empty cells black to create a single group of black cells that are all connected to each other through their edges. No 2×2 cell area within the grid contains all black cells. Numbers to the left/top of the grid represent the groups of consecutive black cells which are in that row/column in order, either from left to right or from top to bottom. For example, a clue of “3” means the row or column has three consecutive black cells, and a clue of “3 1” means that the row or column has a group of three consecutive black cells followed by a single black cell, separated by at least one white cell. A question mark (?) represents a group of consecutive black cells whose size is unknown; an asterisk (*) represents any number of unknown groups of black cells, including none at all. (The bold lines dividing some grids into 5×5 blocks are to help with counting.)

Answer String: Enter the length in cells of each of the black segments from left to right for the marked rows, and from top to bottom for the marked columns, going in order from A to B to C to D and separating each row’s entry with a comma. This example has the key “13,1121,311,12”.

(Brief) History of Cross the Streams: Descended from Hanjie/Nonograms and Nurikabe (and less directly from Tapa). The style was first created by Grant Fikes as part of his blog’s experimental Monday Mutants series. Although the author had entertained the idea of removing clues from Hanjie puzzles before, the catalyst for the creation of Cross the Streams was beta-testing the game Knarly Combs, which combines elements of Hanjie, Nurikabe, and Minesweeper. Cross the Streams and related variations have since become a staple of Grant’s blog.

History of this example: This Cross the Streams was originally written by Grant Fikes for Akil Oyunlari and appeared in Issue 76.

Sources for Cross the Streams Puzzles: Follow this link for classic Cross the Streams puzzles on this website and this link for variations on Cross the Streams. If you are new to this puzzle type, here are our easiest Cross the Streams to get started on. More Cross the Streams can also be found on Grant’s blog.

Design rules for contributors: A Grandmaster Cross the Streams will have a unique solution that can be reached by logic alone. Generally, a Grandmaster Cross the Streams should have an interesting solution realized through clever combinations of number, ?, and * clues with thematic presentation of clues preferred. Sizes from 10×10 and above are recommended (maximum aspect ratio of 2:1 if rectangular).