X-Wing Sudoku Strategy

Let’s break down the X-Wing strategy for solving Sudoku puzzles into simpler steps:

How to Identify the X-Wing Pattern

Look for two rows or two columns where a single digit (let’s call it “X”) appears as a candidate in only two cells of each row or column. These cells must be aligned both by row and column, forming a square or rectangle when connected. This alignment creates an “X” shape, hence the name “X-Wing.”

How to Analyze the X-Wing Possibilities

Since the digit “X” has only two possible solutions in the rows or columns under analysis, you can identify two possible sets of solutions for the digit. These sets are formed by the cells that are diagonally opposite to each other within the X-Wing pattern.

Test both configurations to see which one holds true. Regardless of the final answer, the digit “X” cannot be a candidate in the rows or columns connected to the base cells of the X-Wing pattern. Eliminate the digit “X” from any other cells in those rows or columns. Here’s a practical example:

X-Wing Sudoku Example

The number 4 has only two possible solutions within the highlighted columns. The four cells are aligned both by row and column, forming an X-Wing pattern. If the two 4s connected by the dotted line are true, the other pair becomes false, and vice versa. Regardless of the final answer, the number 4 cannot be a candidate in the rows connecting to the base pattern. Thus, the 4 circled in red between the two highlighted yellow cells at the bottom can be eliminated.

Remember that sometimes you might encounter incomplete X-Wing patterns (known as Finned X-Wing). In these cases, one of the vertices of the rectangle/square is missing because the digit is a candidate for more cells in that row/column. Analyze the possibilities based on whether the fins (extra positions for the digit) are true or false.