GraphWithAdjacencyLists.cs

namespace rac.so.bytehaven
{
    public class GraphWithAdjacencyLists
    {
        /* An implementation of the Graph data structure. MIT License.
       Made with ♠ by Racso. https://rac.so | https://github.com/Racso */

        private readonly int initialNeighborsCount;
        private readonly Dictionary<int, List<int>> neighbors;

        public GraphWithAdjacencyLists(int initialNodesCount, int initialNeighborsCount)
        {
            neighbors = new Dictionary<int, List<int>>(initialNodesCount);
            this.initialNeighborsCount = initialNeighborsCount;
        }

        public void AddEdge(int nodeA, int nodeB)
        {
            if (!neighbors.ContainsKey(nodeA))
                neighbors[nodeA] = new List<int>(initialNeighborsCount);

            if (!neighbors.ContainsKey(nodeB))
                neighbors[nodeB] = new List<int>(initialNeighborsCount);

            neighbors[nodeA].Add(nodeB);
            neighbors[nodeB].Add(nodeA);
        }

        public void RemoveEdge(int nodeA, int nodeB)
        {
            if (!neighbors.ContainsKey(nodeA) || !neighbors.ContainsKey(nodeB))
                return;

            neighbors[nodeA].Remove(nodeB);
            neighbors[nodeB].Remove(nodeA);
        }

        public void RemoveNode(int node)
        {
            if (!neighbors.ContainsKey(node))
                return;

            foreach (int neighbor in neighbors[node])
                neighbors[neighbor].Remove(node);

            neighbors.Remove(node);
        }

        public int GetDegree(int node)
            => neighbors.ContainsKey(node) ? neighbors[node].Count : 0;

        public IEnumerable<int> GetNeighbors(int node)
            => neighbors.ContainsKey(node) ? neighbors[node] : Array.Empty<int>();

        public IEnumerable<int> GetNodes()
            => neighbors.Keys;

        public int GetNodeCount()
            => neighbors.Count;
    }
}