The Ninth Number Of The Grid
When you have 8 of the same number in any combination of 8 of the 9by9 squares, you can always put the ninth number using the scanning method.
For example, let's say you have the number 4 in place in any 8 squares, you just use the scanning method to place the number 4 in the square where it was missing.
Try it, it's always works, that's a good help toward the solution.
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