public void AddsEdges()
{
var graph = new WeightedSimpleGraph <int>(5);
Assert.AreEqual(0, graph.Vertices[0].Degree);
Assert.AreEqual(0, graph.Vertices[1].Degree);
graph.AddEdge(0, 1, 99);
Assert.AreEqual(1, graph.Vertices[0].Degree);
Assert.AreEqual(1, graph.Vertices[1].Degree);
Assert.AreEqual(1, graph.Vertices[0].Neighbors.Single().ID);
Assert.AreEqual(0, graph.Vertices[1].Neighbors.Single().ID);
Assert.AreEqual(99, graph.Vertices[0].Neighbors.Single().GetEdgeWeight(0));
Assert.AreEqual(99, graph.Vertices[1].Neighbors.Single().GetEdgeWeight(1));
graph.AddEdge(1, 4, 100);
Assert.AreEqual(1, graph.Vertices[0].Degree);
Assert.AreEqual(2, graph.Vertices[1].Degree);
Assert.AreEqual(1, graph.Vertices[4].Degree);
Assert.AreEqual(1, graph.Vertices[0].Neighbors.Single().ID);
Assert.AreEqual(99, graph.Vertices[0].Neighbors.Single().GetEdgeWeight(0));
CollectionAssert.AreEquivalent(new[] { 0, 4 }, graph.Vertices[1].Neighbors.Select(n => n.ID).ToArray());
CollectionAssert.AreEquivalent(new[] { 99, 100 }, graph.Vertices[1].Neighbors.Select(n => n.GetEdgeWeight(1)).ToArray());
Assert.AreEqual(1, graph.Vertices[4].Neighbors.Single().ID);
Assert.AreEqual(100, graph.Vertices[4].Neighbors.Single().GetEdgeWeight(4));
}
// This uses Prim's algorithm: "https://en.wikipedia.org/wiki/Prim's_algorithm. We don't actually need
// to build the MST, just need the total cost of the streets that compose it. The heap itself can be
// used to keep track of which vertices are in the MST. Arbitrarily choose the building/vertex with ID 0
// to begin creating the MST from. Using int.MaxValue as a sentinel value to represent the street cost
// for a building into the growing MST when that building actually has no street into the MST. Hopefully
// that doesn't lead to problems, otherwise would need nullable ints w/ a custom comparer, or something.
public static long Solve(int buildingCount, int[,] streets)
{
var buildingGraph = WeightedSimpleGraph.CreateFromOneBasedEdges(buildingCount, streets);
var connectionCosts = new BinaryHeap(buildingGraph, buildingGraph.Vertices[0]);
long totalStreetCost = 0;
while (!connectionCosts.IsEmpty)
{
var cheapestConnection = connectionCosts.Extract();
var building = cheapestConnection.Key;
int costToConnectBuilding = cheapestConnection.Value;
totalStreetCost += costToConnectBuilding;
foreach (var neighbor in building.Neighbors)
{
int costToConnectNeighborFromBuilding = building.GetEdgeWeight(neighbor);
int currentCostToConnectNeighbor;
// The neighboring building may still be in the heap, or it might already be in the MST. If
// it's still in the heap, check to see if we can improve its cost to get into the MST by
// utilizing its street to the building just added.
if (connectionCosts.TryGetValue(neighbor, out currentCostToConnectNeighbor))
{
if (costToConnectNeighborFromBuilding < currentCostToConnectNeighbor)
{
connectionCosts.Update(neighbor, costToConnectNeighborFromBuilding);
}
}
}
}
return(totalStreetCost);
}
private static void Main()
{
int remainingTestCases = FastIO.ReadNonNegativeInt();
while (remainingTestCases-- > 0)
{
int cityCount = FastIO.ReadNonNegativeInt();
int highwayCount = FastIO.ReadNonNegativeInt();
int startCityIndex = FastIO.ReadNonNegativeInt() - 1;
int endCityIndex = FastIO.ReadNonNegativeInt() - 1;
var cityGraph = new WeightedSimpleGraph(cityCount);
for (int h = 0; h < highwayCount; ++h)
{
cityGraph.AddEdge(
firstVertexID: FastIO.ReadNonNegativeInt() - 1,
secondVertexID: FastIO.ReadNonNegativeInt() - 1,
weight: FastIO.ReadNonNegativeInt());
}
int?totalMinutes = HIGHWAYS.Solve(cityGraph,
startCity: cityGraph.Vertices[startCityIndex],
endCity: cityGraph.Vertices[endCityIndex]);
Console.WriteLine(totalMinutes?.ToString() ?? "NONE");
}
}
public void ValidatesAGraph2()
{
// This graph is two lines and a point.
var graph = WeightedSimpleGraph <int> .CreateFromOneBasedEdges(5, new[, ]
{
{ 1, 2, 10 }, { 3, 4, 11 }
});
Assert.AreEqual(1, graph.Vertices[0].Degree);
Assert.AreEqual(1, graph.Vertices[1].Degree);
Assert.AreEqual(1, graph.Vertices[2].Degree);
Assert.AreEqual(1, graph.Vertices[3].Degree);
Assert.AreEqual(0, graph.Vertices[4].Degree);
Assert.IsTrue(graph.HasEdge(0, 1));
Assert.IsTrue(graph.HasEdge(2, 3));
Assert.IsFalse(graph.HasEdge(2, 0));
Assert.IsFalse(graph.HasEdge(0, 3));
Assert.IsFalse(graph.HasEdge(1, 2));
Assert.IsFalse(graph.HasEdge(3, 1));
for (int i = 0; i <= 4; ++i)
{
Assert.IsFalse(graph.HasEdge(4, i));
}
Assert.IsFalse(graph.Vertices[0].HasNeighbor(0));
Assert.IsTrue(graph.Vertices[0].HasNeighbor(1));
Assert.IsFalse(graph.Vertices[0].HasNeighbor(2));
Assert.IsFalse(graph.Vertices[0].HasNeighbor(3));
Assert.IsFalse(graph.Vertices[0].HasNeighbor(4));
Assert.IsTrue(graph.Vertices[1].HasNeighbor(0));
Assert.IsFalse(graph.Vertices[1].HasNeighbor(1));
Assert.IsFalse(graph.Vertices[1].HasNeighbor(2));
Assert.IsFalse(graph.Vertices[1].HasNeighbor(3));
Assert.IsFalse(graph.Vertices[1].HasNeighbor(4));
Assert.IsFalse(graph.Vertices[2].HasNeighbor(0));
Assert.IsFalse(graph.Vertices[2].HasNeighbor(1));
Assert.IsFalse(graph.Vertices[2].HasNeighbor(2));
Assert.IsTrue(graph.Vertices[2].HasNeighbor(3));
Assert.IsFalse(graph.Vertices[2].HasNeighbor(4));
Assert.IsFalse(graph.Vertices[3].HasNeighbor(0));
Assert.IsFalse(graph.Vertices[3].HasNeighbor(1));
Assert.IsTrue(graph.Vertices[3].HasNeighbor(2));
Assert.IsFalse(graph.Vertices[3].HasNeighbor(3));
Assert.IsFalse(graph.Vertices[3].HasNeighbor(4));
Assert.IsFalse(graph.Vertices[4].HasNeighbor(0));
Assert.IsFalse(graph.Vertices[4].HasNeighbor(1));
Assert.IsFalse(graph.Vertices[4].HasNeighbor(2));
Assert.IsFalse(graph.Vertices[4].HasNeighbor(3));
Assert.IsFalse(graph.Vertices[4].HasNeighbor(4));
Assert.AreEqual(10, graph.Vertices[0].GetEdgeWeight(1));
Assert.AreEqual(11, graph.Vertices[2].GetEdgeWeight(3));
}
// For example, an edge like (1, 2, 4) => there's an edge between vertices 0 and 1 with weight 4.
public static WeightedSimpleGraph CreateFromOneBasedEdges(int vertexCount, int[,] edges)
{
var graph = new WeightedSimpleGraph(vertexCount);
for (int i = 0; i < edges.GetLength(0); ++i)
{
graph.AddEdge(edges[i, 0] - 1, edges[i, 1] - 1, edges[i, 2]);
}
return(graph);
}
// This uses Dijkstra's algorithm: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm.
// We return immediately upon visiting the destination intersection, and we don't initialize
// the heap with all intersections. We only add intersections to the heap when reaching one
// of their neighbor intersections. Without a pre-filled heap to rely on, we track what
// intersections have been visited using an array of bools.
public static double Solve(WeightedSimpleGraph intersectionGraph)
{
var startIntersection = intersectionGraph.Vertices.First();
var endIntersection = intersectionGraph.Vertices.Last();
var pathSafetyProbabilities = new BinaryHeap(startIntersection, topValue: 1);
bool[] visitedIntersections = new bool[intersectionGraph.VertexCount];
while (!pathSafetyProbabilities.IsEmpty)
{
// Instead of choosing the closest neighbor, we choose the safest (highest probability).
var safestPath = pathSafetyProbabilities.Extract();
var intersection = safestPath.Key;
double safetyProbabilityToIntersection = safestPath.Value;
if (intersection == endIntersection)
{
return(safetyProbabilityToIntersection * 100);
}
foreach (var neighbor in intersection.Neighbors.Where(n => !visitedIntersections[n.ID]))
{
double safetyProbabilityToNeighborThroughIntersection = safetyProbabilityToIntersection
* (intersection.GetEdgeWeight(neighbor) / (double)100);
double currentSafetyProbabilityToNeighbor;
// We know the neighboring intersection hasn't been visited yet, so we need to maintain
// its safety probability in the heap. If it's already in the heap, see if a safer path
// exists to it through the intersection we're visiting. If it isn't in the heap yet, add it.
if (pathSafetyProbabilities.TryGetValue(neighbor, out currentSafetyProbabilityToNeighbor))
{
if (safetyProbabilityToNeighborThroughIntersection > currentSafetyProbabilityToNeighbor)
{
pathSafetyProbabilities.Update(neighbor, safetyProbabilityToNeighborThroughIntersection);
}
}
else
{
pathSafetyProbabilities.Add(neighbor, safetyProbabilityToNeighborThroughIntersection);
}
}
visitedIntersections[intersection.ID] = true;
}
throw new NotSupportedException();
}
public BinaryHeap(WeightedSimpleGraph graph, Vertex topKey, int topValue = 0)
{
_keyValuePairs.Add(new KeyValuePair <Vertex, int>(topKey, topValue));
_keyIndices.Add(topKey, 0);
foreach (var vertex in graph.Vertices)
{
if (vertex.Equals(topKey))
{
continue;
}
_keyValuePairs.Add(new KeyValuePair <Vertex, int>(vertex, int.MaxValue));
_keyIndices.Add(vertex, _keyValuePairs.Count - 1);
}
}
// This uses Dijkstra's algorithm: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm.
// We return immediately upon visiting the destination city, and we don't initialize the
// heap with all cities. We only add cities to the heap when reaching one of their neighbor
// cities. Without a pre-filled heap to rely on, we track what cities have been visited
// using an array of bools.
public static int?Solve(WeightedSimpleGraph cityGraph, Vertex startCity, Vertex endCity)
{
var pathCosts = new BinaryHeap(startCity);
bool[] visitedCities = new bool[cityGraph.VertexCount];
while (!pathCosts.IsEmpty)
{
var cheapestPath = pathCosts.Extract();
var city = cheapestPath.Key;
int pathCostToCity = cheapestPath.Value;
if (city == endCity)
{
return(pathCostToCity);
}
foreach (var neighbor in city.Neighbors.Where(n => !visitedCities[n.ID]))
{
int pathCostToNeighborThroughCity = pathCostToCity + city.GetEdgeWeight(neighbor);
int currentPathCostToNeighbor;
// We know the neighboring city hasn't been visited yet, so we need to maintain its
// path cost in the heap. If it's already in the heap, see if a cheaper path exists
// to it through the city we're visiting. If it isn't in the heap yet, add it.
if (pathCosts.TryGetValue(neighbor, out currentPathCostToNeighbor))
{
if (pathCostToNeighborThroughCity < currentPathCostToNeighbor)
{
pathCosts.Update(neighbor, pathCostToNeighborThroughCity);
}
}
else
{
pathCosts.Add(neighbor, pathCostToNeighborThroughCity);
}
}
visitedCities[city.ID] = true;
}
return(null);
}
public void TryGetEdgeWeight()
{
var graph = new WeightedSimpleGraph <int>(5);
int value;
bool hasValue;
hasValue = graph.Vertices[0].TryGetEdgeWeight(1, out value);
Assert.AreEqual(0, value);
Assert.IsFalse(hasValue);
graph.AddEdge(0, 3, 99);
hasValue = graph.Vertices[0].TryGetEdgeWeight(3, out value);
Assert.AreEqual(99, value);
Assert.IsTrue(hasValue);
hasValue = graph.Vertices[3].TryGetEdgeWeight(0, out value);
Assert.AreEqual(99, value);
Assert.IsTrue(hasValue);
hasValue = graph.Vertices[0].TryGetEdgeWeight(1, out value);
Assert.AreEqual(0, value);
Assert.IsFalse(hasValue);
}
private static void Main()
{
int intersectionCount;
while ((intersectionCount = FastIO.ReadNonNegativeInt()) != 0)
{
int streetCount = FastIO.ReadNonNegativeInt();
var intersectionGraph = new WeightedSimpleGraph(intersectionCount);
for (int i = 0; i < streetCount; ++i)
{
intersectionGraph.AddEdge(
firstVertexID: FastIO.ReadNonNegativeInt() - 1,
secondVertexID: FastIO.ReadNonNegativeInt() - 1,
weight: FastIO.ReadNonNegativeInt());
}
Console.WriteLine(
$"{CHICAGO.Solve(intersectionGraph):F6} percent");
}
}
public void ValidatesAGraph1()
{
// This graph is a triangle.
var graph = WeightedSimpleGraph <int> .CreateFromZeroBasedEdges(3, new[, ]
{
{ 0, 1, 1 }, { 0, 2, 2 }, { 1, 2, 3 }
});
Assert.AreEqual(2, graph.Vertices[0].Degree);
Assert.AreEqual(2, graph.Vertices[1].Degree);
Assert.AreEqual(2, graph.Vertices[2].Degree);
Assert.IsTrue(graph.HasEdge(0, 1));
Assert.IsTrue(graph.HasEdge(1, 0));
Assert.IsTrue(graph.HasEdge(0, 2));
Assert.IsTrue(graph.HasEdge(1, 2));
Assert.IsFalse(graph.HasEdge(1, 1));
Assert.IsFalse(graph.Vertices[0].HasNeighbor(0));
Assert.IsTrue(graph.Vertices[0].HasNeighbor(1));
Assert.IsTrue(graph.Vertices[0].HasNeighbor(2));
Assert.IsTrue(graph.Vertices[1].HasNeighbor(0));
Assert.IsFalse(graph.Vertices[1].HasNeighbor(1));
Assert.IsTrue(graph.Vertices[1].HasNeighbor(2));
Assert.IsTrue(graph.Vertices[2].HasNeighbor(0));
Assert.IsTrue(graph.Vertices[2].HasNeighbor(1));
Assert.IsFalse(graph.Vertices[2].HasNeighbor(2));
Assert.AreEqual(1, graph.Vertices[0].GetEdgeWeight(1));
Assert.AreEqual(2, graph.Vertices[0].GetEdgeWeight(2));
Assert.AreEqual(1, graph.Vertices[1].GetEdgeWeight(0));
Assert.AreEqual(3, graph.Vertices[1].GetEdgeWeight(2));
Assert.AreEqual(2, graph.Vertices[2].GetEdgeWeight(0));
Assert.AreEqual(3, graph.Vertices[2].GetEdgeWeight(1));
}
internal Vertex(WeightedSimpleGraph graph, int ID)
{
_graph = graph;
this.ID = ID;
}