To solve easy sudoku puzzles @ thesudoku.app, you will need to use only «singles» technique, the most elementary solving technique.
A «hidden single» is a single candidate remaining for entire row, column or 3x3 unit. In other words, only one cell is left to place that candidate.
Hidden single in 3x3 unit
Take a look at the highlighted unit. Then take a look at row
B and column 1, each contains digit 3. This means that the only candidate for cell C3 is digit 3. Figure 1. Hidden single in 3x3 unit Solve puzzle from the Figure 1 Hidden single in a row
Take a look at row
F. Then take a look at the 3x3 unit and highlighted column 6, each contains digit 1. This means that the only candidate for cell F4 in row F is digit 1. Figure 2. Hidden single in a row Solve puzzle from the Figure 2 Hidden single in a column
Take a look at column
4. Then take a look at highlighted 3x3 unit and highlighted rows C and I, each contains digit 1. This means that the only candidate for cell H4 in column 4 is digit 1. Figure 3. Hidden single in a column Solve puzzle from the Figure 3
A «naked single» is the last remaining candidate in a cell. In other words, a single becomes «naked» when all other candidates have been eliminated from its cell.
Take a look at the highlighted 3x3 unit, remaining digits to fill this unit are
1, 2 and 3. Then take a look at row B. Digits 2 and 3 are already in this row. This fact eliminates these digits from cell B3. This means that the last remaining candidate for cell B3 is 1. Figure 4. Naked single Solve puzzle from the Figure 4
Sometimes hidden and naked singles are not so easy to spot. Filling «pencil marks» will definitely help you to solve any sudoku puzzle. Pencil marks represents remaining candidates in each cell. Filling in all the pencil marks for every cell is quite a laborious task. thesudoku.app «autofill» feature will do it for you, just open «three dots» menu and click «Autofill notes»
Take a look at the filled grid. Now you can easily spot naked singles
5 in cell C3, 6 in cell G2, 7 in cell H2 and 9 in cell G7. Also take a look at first 3x3 unit, you can easily spot that 2 can only be placed in cell B1, it is hidden single. Figure 5. Using autofill Solve puzzle from the Figure 5