Hitori is quite similar to Sudoku, in that it takes logical deduction to work out which cells to paint out. One strategy is to use Shift-clicking to tag all the repeated numbers in each column, then use Ctrl-clicking to tag all the repeated numbers in each row.

Once this is done for the entire board, the cells which have been tagged both ways are good candidates for painting, although not always. When painting a cell, un-tagging the other cells with the same number in the same row and column as that cell is a good way to keep track of which cells are still violating rule 1 of Hitori.

Always bear in mind that rule 2 of Hitori means that two adjacent cells can’t both be painted. Hitori will highlight in red the cells which violate rule 2. Similarly, groups of cells which violate rule 3 by separating one or more unpainted cells from the other unpainted cells will be highlighted in red.

If you get stuck at any point, press Hint in the header bar for Hitori to hint a cell which should be painted or unpainted to move closer to a solution.