Compen/EE 362
Asst. 8 Solution
Fall 2010
Problem 1.
Text Problem 5.8. Give a simple heuristic for finding two paths
through a network from a given source to a given destination that can
survive the loss of any communication line (if two such paths exist.
Don’t worry about possibility of router crashes.
Give two answers. In one, the answer if one of the alternatives is the least
cost path and the other is as good as possible. In the other answer, don’t
worry about how good the two paths are.
Solution. First case: Pick the least cost route and
remove all lines used for the route from A to B.
Then run the shortest path algorithm to find the
shortest path for this reduced network, if there is
such a path.
Even if there is no path after the least cost
path is removed, it still is possible to find two
paths.
In general, assume there is at least one path
from A to B. To see if two paths are possible,
try to draw a cut that isolates A and B by cutting
only one link. If and only if you can find such a
cut, only one path is possible.
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Assume all cuts pass through 2 or more links.
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 Spring '11
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 Shortest path problem, shortest path algorithm

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