87 lines
2.9 KiB
Markdown
87 lines
2.9 KiB
Markdown
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# Lab 11: Graph Search - Bus Stops
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## Graph Search Basics
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The purpose of this lab is to give you practice implementing graph data
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structures and basic graph traversal and reachability queries.
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You are building an app for a newly created bus system connecting Harrisonburg
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to Charlottesville. There are many different bus routes each of which travels
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between named stops along its route. Not all of the bus routes cross each other,
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so it is possible that there are some pairs of stops where there is no way of
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getting on a bus at the first stop and making changes to get to the final stop.
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Your task is to implement a graph search function that can determine a sequence
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of stops a user can use to get from a starting stop to an ending stop, or to
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tell the user that there is no bus route possible between those two stops.
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## Input
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The bus route segments are described as single stretches of road between two
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consecutive stops. All such pairs will be described in one direction, but all
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bus routes are bidirectional, since buses travel in both directions along each
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route.
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The first line of input has an integer n that is the number of road segments
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between consecutive stops. The next n lines of input describe the consecutive
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stops, each of which is named by a string of alphabetical characters with no
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spaces. The line will contain both of the stops of the segment, separated by a
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space.
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The final line of input is the query, which is two stop names separated by a
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space.
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## Output
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Give a sequence of stop names starting at the starting stop of the query and
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ending at the ending stop separated by spaces (if one exists), or output "no
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route possible" if none is found.
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<table>
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<tr>
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<td>Sample Input</td>
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<td>Sample Output</td>
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</tr>
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<tr>
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<td><pre>
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2
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Hburg JMU
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Charlottesville JMU
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Hburg Charlottesville</pre></td>
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<td><pre>Hburg JMU Charlottesville</pre></td>
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</tr>
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<tr>
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<td><pre>
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4
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Hburg JMU
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JMU Upark
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Upark Hburg
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CVO UVA
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Hburg UVA</pre></td>
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<td><pre>no route possible</pre></td>
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</tr>
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</table>
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Larger example files (the one used on Gradescope) can be downloaded here:
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bus_stops_t3_in.txt Download bus_stops_t3_in.txt bus_stops_t3_exp.txt Download
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bus_stops_t3_exp.txt Depending how you implement your graph, the order of stops
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on the path may not be unique, so, checking your solution requires writing a bit
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more code to validate your path (and of course, that is optional).
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## Hints:
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- Store the stops in a dictionary and use a set for the edge list.
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- You will need to implement a method that uses a spanning tree. The lab is
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asking you for a path between the locations (not necessarily the shortest
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path).
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## Submission:
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Your code in a file name `cs412_bus_stops_a.py` and submit your code to
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gradescope.
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## Rubrics:
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- (6 points) program solves the examples
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- (3 points) solves the hidden examples
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- (1 point) instructor review
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