By using ghost numbers, you will fill in two digits almost completely around the entire grid. (Those are his ratings maximum "bombs" are nine in this particular collection.) I chose this because it is probably the easiest X-Wing to spot that I have ever encountered. The first Sudoku is based on a "7 bomb" "difficult" puzzle by Tetsuya Nishio. If the calculation for B and E is a two digit number, take the final digit. Then the cache is at N 37 33.ABC W 122 18.DEF. Let the larger X-Wing digit in the first be Q. The first one has not one but two X-Wings in it. In the first example above, the digit is 4. Now for the puzzle! Every X-Wing relies on a single digit. ![]() The name "X-Wing" comes from the typical X pattern formed by each of these corners. The potential cells must form the corners of a rectangle. The SAME digit must be restricted to ONE of TWO squares in a different row (or column).ģ. A single digit must be restricted to ONE of TWO squares in a row (or column).Ģ. Here are the ingredients for spotting an X-Wing. (Now you have a 1-3 double in the top row, eliminating the 3 from the upper left pink cell and leaving a 7) That is enough information to solve the rest of the puzzle. We do not which goes where right now, but we do know one additional fact: There cannot be a 5 in either of the pink cells. If the 5 goes in a dark blue cell, it must also go in the other dark blue cell. We Don't know what goes where, but we know one thing for certain: If a 5 goes in a light blue cell, it must also go in the other light blue cell. Much of the puzzle has been filled in, but we now hit a wall if we only know basic and intermediate methods. Here is a full puzzle, adapted from a computer program that I have. This information may be enough to solve the puzzle. Therefore, even though we cannot place the 4 in the correct square, we know that we cannot place a 4 in any of the cells with an X in them. Now, remember that It is impossible for more than one 4 to be in the same row. If the 4 is in one tan square, it must be in the other tan square. However, we know one fact for certain: If 4 is in one yellow square, it must be in the other yellow square as well. In the second column, all digits are again filled in except the yellow/tan squares, each of which must contain a 2 or a 4. Each must contain a 4 or an 8, but we don't know which goes where. Often this information will allow you to fill in a different cell and then complete the puzzle.Ĭonsider the following grid: In the first numbered column, all digits are filled in except the yellow/tan cells. X-Wing is not a strategy to enter a digit in the indicated cells but rather a way to eliminate a digit elsewhere on the grid. ![]() If you can wrap your head around this method, you'll start to develop ways of thinking that will allow you to pick up the rest of the strategies. The first advanced strategy to learn is X-Wing. ![]() If you progress beyond the easy and easy-intermediate stage, you will discover that there is an elegance and poetry to solving Sudoku that goes beyond mere counting and filling in the missing digit. ![]() The second is to teach some advanced methods for solving Sudoku. The first is to confound the programmers and get you to actually solve these the way they are supposed to be solved. This is the beginning of a series of puzzles that have two goals. If you've been paying attention to my previous puzzles, you'll know that I disapprove of such measures. They'd rather run write a computer program and let it fill in the blanks. The dark side is that some people don't want to solve the puzzle. Why not? All you have to do is solve a straight-forward Sudoku puzzle, grab the digits, and plug them into the coordinates. Puzzle cachers just LOVE Sudoku (although the craze may have passed).
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