Cell

1. click

1.1. has number

1.1.1. fill replace

1.2. no number

1.2.1. make selected cell

1.2.1.1. calculate all of proper numbers

1.2.2. fill row & col

1.2.3. enable input box

1.2.3.1. click

1.2.3.1.1. what cell selected?

1.2.3.1.2. what number clicked?

1.2.3.1.3. insert number into selected cell