问题
Let's say I have the following CSV
Sydney,Dubai,1
Dubai,Venice,2
Venice,Rio,3
Venice,Sydney,1
Sydney,Rio,7
First field is From second is To and third is Duration.
I need a method which can take a From input and spit out the shortest path to all other To field in the following format-
Selected City: Sydney
To 1: Dubai, Smallest Path Length: 1, Path: Sydney, Dubai.
To 2: Venice, Smallest Path Length: 3, Path: Sydney, Dubai, Venice.
To 3: Rio, Smallest Path Length: 6, Path: Sydney, Dubai, Venice, Rio.
(N.B. Sydney-Rio is 7 hours long hence Sydney-Dubai-Venice-Rio
is the shortest route here which takes 2 hours).
I haven't got any code to add here plus others have suggested to use Dijkstra's algorithm but so far I haven't got an example which accomplishes what I need.
回答1:
I have written a small console program which satisfies your need. it is very basic and ca be enhanced further if needed.
if you need a downloadable solution please let me know.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ShortPath
{
class Program
{
static void Main(string[] args)
{
// assuming you have loaded your CSVs into a list of string
List<string> csvLines = new List<string>()
{
"Sydney,Dubai,1",
"Dubai,Venice,2",
"Venice,Rio,3",
"Venice,Sydney,1",
"Sydney,Rio,7"
};
// lets convert the list of string into list or route
var routes = new List<Route>();
csvLines.ForEach(s =>
{
// split by ,
string[] pieces = s.Split(',');
// ensure travel time is a number
decimal travelTime = 0;
decimal.TryParse(pieces[2], out travelTime);
// convert string to route object
routes.Add(new Route()
{
From = pieces[0],
To = pieces[1],
TravelTime = travelTime
});
});
// once all the data in place - the rest is easy.
// lets assume our FROM is sydne
string selectedFrom = "Sydney";
// no lets find all the routes from sydney to every other place
// listing the shortes route first
// the "Where" clause allows us to filter by the selected from
// the order by clause allows us to order by travel time
var desiredRoutes = routes.Where(route => route.From == selectedFrom).OrderBy(route => route.TravelTime).ToList();
// the output template allows us to format all outputs
// the numbers in culry bracers such as {0} {1}...etc are placeholderst that get replaced with actul values
// {0} = index number
// {1} = To
// {2} = duration
// {3} = From
// "To 1: Dubai, Smallest Path Length: 1, Path: Sydney, Dubai.";/
string outputTemplate = "To {0}: {1}, Smallest Path Length: {2}, Path: {3}, {1}.";
Console.WriteLine("Selected Country: '{0}'.", selectedFrom);
// look through each selected route
for(int index = 0; index < desiredRoutes.Count; index++)
{
// ensure you access to the route variable in the current instance of the loop
var route = desiredRoutes[index];
// write all outputs
// (index + 1) allows our counter to start from 1 instead of 0
Console.WriteLine(outputTemplate, (index + 1), route.To, route.TravelTime, route.From);
}
Console.WriteLine("Press any key to exit.");
Console.ReadKey();
}
}
}
NOTE: the class for Route:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ShortPath
{
public class Route
{
public string From { get; set; }
public string To { get; set; }
public decimal TravelTime { get; set; }
}
}
The output should look as follows:
Selected Country: 'Sydney'.
To 1: Dubai, Smallest Path Length: 1, Path: Sydney, Dubai.
To 2: Rio, Smallest Path Length: 7, Path: Sydney, Rio.
Press any key to exit.
回答2:
Try this
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
//this one uses strings as node names
Dijkstra1.Program.Dijkstra();
Console.ReadLine();
}
}
}
namespace Dijkstra1
{
class Program
{
//Sydney,Dubai,1
//Dubai,Venice,2
//Venice,Rio,3
//Venice,Sydney,1
//Sydney,Rio,7
static List<List<String>> input1 = new List<List<string>>{
new List<String>() {"Sydney","0","1","7","1"},
new List<String>() {"Dubai", "1","0","0","2"},
new List<String>() {"Rio", "7","0","0","3"},
new List<String>() {"Venice","1","2","3","0"},
};
static public void Dijkstra()
{
CGraph cGraph;
cGraph = new CGraph(input1);
Console.WriteLine("-------------Input 1 -------------");
cGraph.PrintGraph();
}
class CGraph
{
List<Node> graph = new List<Node>();
public CGraph(List<List<String>> input)
{
foreach (List<string> inputRow in input)
{
Node newNode = new Node();
newNode.name = inputRow[0];
newNode.distanceDict = new Dictionary<string, Path>();
newNode.visited = false;
newNode.neighbors = new List<Neighbor>();
//for (int index = 1; index < inputRow.Count; index++)
//{
// //skip diagnol values so you don't count a nodes distance to itself.
// //node count start at zero
// // index you have to skip the node name
// //so you have to subtract one from the index
// if ((index - 1) != nodeCount)
// {
// string nodeName = input[index - 1][0];
// int distance = int.Parse(inputRow[index]);
// newNode.distanceDict.Add(nodeName, new List<string>() { nodeName });
// }
//}
graph.Add(newNode);
}
//initialize neighbors using predefined dictionary
for (int nodeCount = 0; nodeCount < graph.Count; nodeCount++)
{
for (int neighborCount = 0; neighborCount < graph.Count; neighborCount++)
{
//add one to neighbor count to skip Node name in index one
if (input[nodeCount][neighborCount + 1] != "0")
{
Neighbor newNeightbor = new Neighbor();
newNeightbor.node = graph[neighborCount];
newNeightbor.distance = int.Parse(input[nodeCount][neighborCount + 1]);
graph[nodeCount].neighbors.Add(newNeightbor);
Path path = new Path();
path.nodeNames = new List<string>() { input[neighborCount][0] };
//add one to neighbor count to skip Node name in index one
path.totalDistance = int.Parse(input[nodeCount][neighborCount + 1]);
graph[nodeCount].distanceDict.Add(input[neighborCount][0], path);
}
}
}
foreach (Node node in graph)
{
foreach (Node nodex in graph)
{
node.visited = false;
}
TransverNode(node);
}
}
public class Neighbor
{
public Node node { get; set; }
public int distance { get; set; }
}
public class Path
{
public List<string> nodeNames { get; set; }
public int totalDistance { get; set; }
}
public class Node
{
public string name { get; set; }
public Dictionary<string, Path> distanceDict { get; set; }
public bool visited { get; set; }
public List<Neighbor> neighbors { get; set; }
}
static void TransverNode(Node node)
{
if (!node.visited)
{
node.visited = true;
foreach (Neighbor neighbor in node.neighbors)
{
TransverNode(neighbor.node);
string neighborName = neighbor.node.name;
int neighborDistance = neighbor.distance;
//compair neighbors dictionary with current dictionary
//update current dictionary as required
foreach (string key in neighbor.node.distanceDict.Keys)
{
if (key != node.name)
{
int neighborKeyDistance = neighbor.node.distanceDict[key].totalDistance;
if (node.distanceDict.ContainsKey(key))
{
int currentDistance = node.distanceDict[key].totalDistance;
if (neighborKeyDistance + neighborDistance < currentDistance)
{
List<string> nodeList = new List<string>();
nodeList.AddRange(neighbor.node.distanceDict[key].nodeNames);
nodeList.Insert(0, neighbor.node.name);
node.distanceDict[key].nodeNames = nodeList;
node.distanceDict[key].totalDistance = neighborKeyDistance + neighborDistance;
}
}
else
{
List<string> nodeList = new List<string>();
nodeList.AddRange(neighbor.node.distanceDict[key].nodeNames);
nodeList.Insert(0, neighbor.node.name);
Path path = new Path();
path.nodeNames = nodeList;
path.totalDistance = neighbor.distance + neighborKeyDistance;
node.distanceDict.Add(key, path);
}
}
}
}
}
}
public void PrintGraph()
{
foreach (Node node in graph)
{
Console.WriteLine("Node : {0}", node.name);
foreach (string key in node.distanceDict.Keys.OrderBy(x => x))
{
Console.WriteLine(" Distance to node {0} = {1}, Path : {2}", key, node.distanceDict[key].totalDistance, string.Join(",", node.distanceDict[key].nodeNames.ToArray()));
}
}
}
}
}
}
来源：https://stackoverflow.com/questions/39561207/shortest-path-finder-from-csv-in-c-sharp