#Times sudoku how to

We eliminate repeated digits when considering digits of two or three zones together. Set union is technical, but this we do by common sense and do naturally. Unique set of existing digits in all these three together are, It is in three zones or areas - row R2, column C5 and 9 cell top-middle major square. Target is to get two-digit possibilities first. We'll select relatively more promising cells in a row, a column or a 9 cell square (each a zone) to evaluate the smallest length of possible digits in the cells first. To skip the section, click here.ĭSA technique - Enumerating digits possible for an empty cell: If number of digits possible is 1, we get a valid cell hitĪfter speed of solution, reducing labor being the main objective, we won't enumerate 4 or 5-digit possibilities or enumerate possible digits for ALL the cells. Section below explains in a bit of detail the process of enumerating digits possible in a cell. This is a breakthrough by single digit lock and DSA. Identify a second Single digit lock on 5 in R9C5, R9C6 by scan for 5 in R7, C4 - R9C1 3 by possible digit DS elimination of 5 (because of single digit lock on 5 in R9) from possible digit subset in R9C1 (because of in C1).

Note: For more details, you may click on the section link on 'How the parallel digit scan works' above and return by clicking on browser back button. Next identify the advanced technique of Parallel scan for 8 on empty cells of R8: 8 in bottom left major square eliminates R8C1, R8C2, R8C3 for 8 and 8 in C9 eliminates R8C9 for 8 leaving the single cell R8C7 for 8 - R8C7 8.

Never let go of an effective single digit lock. In this case we get the breakthrough of R9C2 6 by scan for 6 in R7, R8 and C1, 6 in R7 being actually a lock on digit 6.Ī single digit lock is always a valuable asset for hard Sudoku simplification and whenever yoi identify such a possibility, just note it in your mind for future use at the right timer. Reduction of instances of 6 from all such empty cells is the gain.Īlternately this lock on 6 acts as if 6 actually exists in R8 and that's why a lock on a digit can be used for a scan for the digit. In the final solution, 6 can appear in only one of these two cells and in no other cell of the parent bottom right major square or the parent row R8. In this case observe that by scan for 6 in R8, digit placement of digit 6 is restricted to only two cells in R8, R8C7 and R8C9. Identify Single digit lock on 6 in R7C7, R7C9 by scan for 6 in R8 - this lock on 6 participates in next valid cell R9C2 6 by scan for 6 in R7 by the lock, 6 in R8 and 6 in C1.Īn effective single digit lock is formed invariably by scan for a digit in a single column or row or more frequently by cross-scan over a row and a column. No more digits can be placed by this simple method of row-column scan at this point. Look for placing any other possible digit by row-column scan.Īn easy catch by opportunistic scan for 9: R9C9 9 by scan in R7, R8. No more easy valid digit 3 possible at this point. R2C3 3 by row column scan for 3 in R1, R3, C2 - R6C7 3 by scan for 3 in R4, R5, C9 - R8C8 3 by scan in C7, C9. In this game having no success with 1 or 2 by row column scan select digit 3 as promising and get a few easy placements. That's why though we start a Sudoku hard solution with systematic row column scan, we also look for other advanced digit patterns for early breakthroughs of valid digits. But when you face a Sudoku hard, valid cell by row column scan may be few or non-existent to start with. Then start the process for the next higher digit.įor easier lower level Sudoku games this systematic method of row column scan should provide a smooth path to the final solution. With this basic concept in place start row column scan for the lowest digit 1 and continue the process till a digit is finished or ends in a block of no more success. Identify the rows and columns with the digit that intersect in a cell in the the 9 square major square. To be quick select the digit that appears maximum number of times and select a promising 9 cell major square for row column scan on its empty cells. Every such easy fill at this stage is a bonus.

Fill as many cells as you can by row-column scan. Use row-column scan, the simplest method to get a unique digit for a cell. Solution to the New York Times Sudoku Hard, 15th February, 2021: Stage 1: Early breakthroughs by Single digit lock and parallel scan To solve quickly you need to concentrate. The New York Times Sudoku Hard, 15th February, 2021

#Times sudoku how to

Solution to New York Times Sudoku hard, 15th February, 2021 explains step by step how to use Sudoku hard techniques to achieve quick breakthroughs. New York Times Sudoku Hard 15th February, 2021 Solved in quick easy steps