Algorithm X
Killer Sudoku Extreme Challenge
Puzzle: Killer Sudoku Extreme Challenge
Author: @Timinator
Published Difficulty: Hard
Algorithm X Complexity: It Depends
Strategy
In Killer Sudoku Extreme Challenge, your algorithm needs to solve up to 40 Expert Killer Sudoku grids. You will need to do everything you did to solve the original Killer Sudoku Solver puzzle and more. You must find some amount of problem-space reduction that makes each grid fairly easy for Algorithm X. When solving 40 puzzles, there is not enough time for Algorithm X to do too much backtracking.
Solving Every Grid Logically
Backtracking involves making a guess and then backing up if that guess leads to a dead end or the path has been fully explored. It is possible to solve every Killer Sudoku grid in the puzzle without making a single guess. In the original puzzle, did you use a class structure similar to this?
A SudokuGroup could be a row, a column or a box. All SudokuGroups behave identically. Cages are another way to group cells and these groups have significantly different behavior which calls for a separate class. If you study how cells behave on a Killer Sudoku grid, you will find even more interesting behavior that can help you find the values of more unknown cells. For an example, click below.
Spoiler Alert: Creating Even More Groups for Killer Sudoku
A Cage is a group of cells that must add up a certain amount. There are other groups of cells that also must add to a certain amount. For instance, all rows, all columns and all boxes add up to 45 since they each must contain the numbers 1 to 9. That is not all that interesting, nor helpful. However, there are more interesting groups of cells that must add up to certain amounts. Can you find those groups?