For this example we'll use a 5 x 5 board because this size requires the fewest number of
tentative Queen placements (only 15) to reach the first solution to the puzzle.
A Queen shown in RED is obviously clashing with at least one previously-placed Queen.
It will be lifted off the board and set down again (or be "placed") in the next unoccupied square.
When a Queen is placed with no clashes on any row, we immediately move up to the next row.
We have FOUND the first possible solution to the 5 x 5 version of the N-Queens puzzle!
This example also shows that when placing Queens in this manner, no 'earlier' solutions can exist.
15 The 15th 'placement' of a Queen
results in this first solution to our puzzle.
5 Number of times a Queen was placed on the board,
and was allowed to stay.
10 Number of times a Queen was placed on the board, but was
clearly challenged by at least one previously-placed Queen.
Queen-placement example page 15 of 15
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by Colin S Pearson and Martin S Pearson
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