Add Dijkstra in C# (#4875)

Author: pascalecu

archive/c/c-sharp/Dijkstra.cs

@@ -0,0 +1,121 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+public static class Program
+{
+    private const int INF = 0x3F3F3F3F;
+
+    private static void ShowUsage()
+    {
+        Console.Error.WriteLine("Usage: please provide three inputs: a serialized matrix, a source node and a destination node");
+        Environment.Exit(1);
+    }
+
+    private static List<int> ParseIntegerList(string input)
+    {
+        if (string.IsNullOrWhiteSpace(input))
+            ShowUsage();
+
+        var list = input
+            .Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+            .Select(s =>
+            {
+                if (!int.TryParse(s, out var val) || val < 0)
+                    ShowUsage();
+                return val;
+            })
+            .ToList();
+
+        if (list.Count == 0)
+            ShowUsage();
+
+        return list;
+    }
+
+    private static int GetMatrixDimension(List<int> matrix)
+    {
+        var length = matrix.Count;
+        var dimension = (int)Math.Sqrt(length);
+        return (dimension * dimension == length && dimension > 0) ? dimension : -1;
+    }
+
+    private static int Dijkstra(List<int> matrix, int dimension, int source, int destination)
+    {
+        var dist = Enumerable.Repeat(INF, dimension).ToArray();
+        var visited = new bool[dimension];
+
+        dist[source] = 0;
+
+        for (int _ = 0; _ < dimension; _++)
+        {
+            int minDist = INF;
+            int minIndex = -1;
+
+            for (int j = 0; j < dimension; j++)
+            {
+                if (!visited[j] && dist[j] < minDist)
+                {
+                    minDist = dist[j];
+                    minIndex = j;
+                }
+            }
+
+            if (minIndex == -1)
+                break;
+
+            if (minIndex == destination)
+                return dist[minIndex];
+
+            visited[minIndex] = true;
+
+            for (int j = 0; j < dimension; j++)
+            {
+                int weight = matrix[minIndex * dimension + j];
+                if (!visited[j] && weight > 0 && dist[minIndex] + weight < dist[j])
+                {
+                    dist[j] = dist[minIndex] + weight;
+                }
+            }
+        }
+
+        return dist[destination] == INF ? -1 : dist[destination];
+    }
+
+    public static int Main(string[] args)
+    {
+        if (args.Length != 3)
+        {
+            ShowUsage();
+        }
+
+        var matrixStr = args[0].Trim();
+        var sourceStr = args[1].Trim();
+        var destinationStr = args[2].Trim();
+
+        if (string.IsNullOrEmpty(matrixStr) || string.IsNullOrEmpty(sourceStr) || string.IsNullOrEmpty(destinationStr))
+            ShowUsage();
+
+        var matrix = ParseIntegerList(matrixStr);
+        int dimension = GetMatrixDimension(matrix);
+
+
+        bool sourceParsed = int.TryParse(sourceStr, out int source);
+        bool destinationParsed = int.TryParse(destinationStr, out int destination);
+
+        if (dimension == -1 || !sourceParsed || !destinationParsed ||
+            source < 0 || source >= dimension ||
+            destination < 0 || destination >= dimension)
+        {
+            ShowUsage();
+        }
+
+        int shortestDistance = Dijkstra(matrix, dimension, source, destination);
+
+        if (shortestDistance == -1)
+            ShowUsage();
+
+        Console.WriteLine(shortestDistance);
+        return 0;
+    }
+}