Add Minimum Spanning Tree in C# (#4878)

Author: pascalecu

archive/c/c-sharp/MinimumSpanningTree.cs

@@ -0,0 +1,108 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+public static class Program
+{
+    private static void ShowUsage()
+    {
+        Console.Error.WriteLine("Usage: please provide a comma-separated list of integers");
+        Environment.Exit(1);
+    }
+
+    private static List<int> ParseIntegerList(string input)
+    {
+        if (string.IsNullOrWhiteSpace(input))
+            ShowUsage();
+
+        var tokens = input
+            .Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+
+        if (tokens.Length < 4) // Minimum size for a 2x2 matrix
+            ShowUsage();
+
+        var numbers = new List<int>();
+        foreach (var token in tokens)
+        {
+            if (!int.TryParse(token, out int value))
+                ShowUsage();
+
+            numbers.Add(value);
+        }
+
+        int dim = (int)Math.Sqrt(numbers.Count);
+        if (dim * dim != numbers.Count)
+            ShowUsage();
+
+        return numbers;
+    }
+
+    private static int MinimumSpanningTreeWeight(List<int> adjacencyMatrix, int dimension)
+    {
+        var includedInMST = new bool[dimension];
+        var minEdgeWeight = new int[dimension];
+
+        for (int i = 0; i < dimension; i++)
+        {
+            minEdgeWeight[i] = int.MaxValue;
+            includedInMST[i] = false;
+        }
+
+        minEdgeWeight[0] = 0;
+        int totalWeight = 0;
+
+        for (int count = 0; count < dimension; count++)
+        {
+            int currentMinWeight = int.MaxValue;
+            int currentNode = -1;
+
+            for (int i = 0; i < dimension; i++)
+            {
+                if (!includedInMST[i] && minEdgeWeight[i] < currentMinWeight)
+                {
+                    currentMinWeight = minEdgeWeight[i];
+                    currentNode = i;
+                }
+            }
+
+            if (currentNode == -1)
+            {
+                ShowUsage();
+            }
+
+            includedInMST[currentNode] = true;
+            totalWeight += currentMinWeight;
+
+            for (int adjacent = 0; adjacent < dimension; adjacent++)
+            {
+                int edgeWeight = adjacencyMatrix[currentNode * dimension + adjacent];
+                if (!includedInMST[adjacent] && edgeWeight != 0 && edgeWeight < minEdgeWeight[adjacent])
+                {
+                    minEdgeWeight[adjacent] = edgeWeight;
+                }
+            }
+        }
+
+        return totalWeight;
+    }
+
+    public static int Main(string[] args)
+    {
+        if (args.Length != 1)
+            ShowUsage();
+
+        var inputList = ParseIntegerList(args[0]);
+
+        var numbers = ParseIntegerList(args[0]);
+        int dimension = (int)Math.Sqrt(numbers.Count);
+
+        int mstWeight = MinimumSpanningTreeWeight(numbers, dimension);
+
+        if (mstWeight == -1)
+            ShowUsage();
+
+        Console.WriteLine(mstWeight);
+
+        return 0;
+    }
+}