👀 Views: 97 💬 Answers: 1 📅 Created: 2025-06-12

algorithm graph dijkstra C#

I'm wondering if anyone has experience with I'm working on a project and hit a roadblock. I'm implementing Dijkstra's Algorithm to find the shortest paths in a weighted graph using C#, but I've encountered unexpected behavior when my graph contains negative edge weights. According to the algorithm, Dijkstra's should only be used with non-negative weights, but I need a way to handle graphs where some edges have negative weights. I've read that the Bellman-Ford algorithm could be more suitable for this case, but I would like to understand why Dijkstra's fails in this scenario and how I might modify my approach. For instance, consider the following implementation: ```csharp public class Graph { private int V; // Number of vertices private List<Tuple<int, int>>[] adj; public Graph(int v) { V = v; adj = new List<Tuple<int, int>>[v]; for (int i = 0; i < v; i++) adj[i] = new List<Tuple<int, int>>(); } public void AddEdge(int u, int v, int w) { adj[u].Add(new Tuple<int, int>(v, w)); } public int[] Dijkstra(int src) { int[] dist = new int[V]; bool[] sptSet = new bool[V]; for (int i = 0; i < V; i++) dist[i] = int.MaxValue; dist[src] = 0; for (int count = 0; count < V - 1; count++) { int u = MinDistance(dist, sptSet); sptSet[u] = true; foreach (var edge in adj[u]) { int v = edge.Item1; int weight = edge.Item2; if (!sptSet[v] && dist[u] != int.MaxValue && dist[u] + weight < dist[v]) dist[v] = dist[u] + weight; } } return dist; } private int MinDistance(int[] dist, bool[] sptSet) { int min = int.MaxValue, minIndex = -1; for (int v = 0; v < V; v++) { if (sptSet[v] == false && dist[v] <= min) { min = dist[v]; minIndex = v; } } return minIndex; } } ``` With the following example graph: ```csharp Graph g = new Graph(5); // Adding edges with negative weights // (0 -> 1, weight 2), (1 -> 2, weight -5), (0 -> 3, weight 1), (3 -> 4, weight 3) g.AddEdge(0, 1, 2); g.AddEdge(1, 2, -5); g.AddEdge(0, 3, 1); g.AddEdge(3, 4, 3); var distances = g.Dijkstra(0); ``` When running this code, I'm getting incorrect shortest path distances, particularly for the vertex `2`, which should be reachable via the negative edge from `1`. However, Dijkstra's seems to overlook this possibility. Can someone explain why this is happening and suggest a better approach to handle graphs with negative weights in C#? Is Bellman-Ford an appropriate alternative here, and if so, could you provide a brief example or point out the differences? For context: I'm using C# on Windows. Thanks in advance! What would be the recommended way to handle this?