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Starvation

The rule for the starvation technique is: if placing a combination of bridges from an island leaves another island with insufficient free bridges, then this combination cannot be placed. Here is an example:

The orange '2' must bridge to the red '2' once, as shown in solid blue. There are three possible combinations of bridges from the orange '2'. Two of these combinations bridge to the red '2', but the third combination bridges to the '2' to the left and the '3' below, as shown in dotted red. If this combination were used, then the '2' highlighted in blue wouldn't have enough free bridges left, and would be "starved". This means that the combination shown in dotted red cannot be correct, so the orange '2' must bridge to the red '2'.

The primary difficulty with the starvation technique is in spotting it. Firstly, you need to know which islands to check for starvation. Islands that can be starved are always neighbours of two of the neighbours of the island we're looking at (so they are always diagonally removed from it). There are therefore up to four possible locations in which an island can be starved from the current position. Here is an example showing potential sites for starvation:

There are four islands, marked in blue, that share two neighbours with the orange '3'. These are then the potential candidates for starvation. At the moment, only the top left blue island can be starved, and the remaining combinations do not share any bridges, so the technique cannot be used. Later on in the game, however, the situation is transformed as follows:

Here, the orange '3' can now be bridged to the red '4' as shown. This is because if we remove the combinations which would starve the blue '1', all the remaining combinations share at least one bridge to the '4'.

Copyright © Adam A. Brown, 2006. www.sudokutiger.com