Hidden triples technique

Strategy #9 for solving Sudoku: Hidden triples technique 

This technique is a logical extension of "Hidden Pairs." This strategy will help you narrow down the number of possible digits in certain cells. It is crucial to understand this strategy and use it in conjunction with other strategies from our blog.

The essence of the "Hidden Triples" tactic is that your game field, apart from the initial digits, should have assumptions of possible digits for each cell. In each 3 by 3 block, you need to try to find a combination of three digits that appears only in these 3 cells and nowhere else. These 3 digits can only be in these 3 cells, so other assumptions can simply be eliminated from these cells.

In the example above on the left, we see the game field on the right where in the ninth 3 by 3 block, we highlighted the triplet of digits 1, 8, 9 (highlighted in red). These three digits are present only in 3 cells, making them unique, and other digits simply cannot be in these cells. Removing the extra digits, we get the result on the game field on the right.

An interesting hint? It's time to test it on online Sudoku! If you have any questions or corrections, write them in the comments.