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Beginner’s Guide to Code Algorithms

56

STEP 17

The second step is to scan the putnumberpresent array to identify the other two

corners.

Once identified, all cells in the same two columns that the corners are in get the

candidate number (putnumber) in each of their cantbelist (remember the array that

stores what the cell cannot be?) except for the corners of the rectangle.

:

:

  For i =​ 1 To 9

  For j =​ 1 To 9

    If putnumberpresent(j, 1) <> “*” And sbox(j, i) =​ ““

      And putnumberpresent(j, i) <> ““ Then

      For k =​ j To 9

        If putnumberpresent(k, i) =​ putnumberpresent(j, i) And k <> j

          And Len(putnumberpresent(j, i)) =​ 2 And putnumberpresent(1, k) <>

“*” Then

          ‘row j,k and columns stored in putnumber are the rectangle

          ‘all cells in the columns of the rectangle except the corners,

          ‘should have putnumber in cantbelist

          For kk =​ 1 To 9

            If kk =​ j Or kk =​ k Then

            Else

              Call addtocantbelist(putnumber, kk, Mid(putnumberpresent(j,

i), 1, 1))

              Call addtocantbelist(putnumber, kk, Mid(putnumberpresent(j,

i), 2, 1))

            End If

          Next kk

        End If

      Next k

    End If

  Next j

  Next i

:

Next putnumber

There are two final algorithms I wanted to present before moving on to Chapter 4

on remote control.

3.7  THE POLYOMINO

The first one is called the algorithm of the polyomino. A polyomino is a two-​dimen­

sional figure that you can form by joining multiple squares. It is derived from the term

domino—​those little squares used in the domino game.

The second is the algorithm of the matching twin.

Here is how the first one works. In the diagram below, 2 is a candidate in exactly two

cells in columns 2, 3, and 6. Notice how they form a closed pattern. The consequence