private readonly Collections.Stack<Integer> _path; // Eulerian path; null if no suh path
#endregion Fields
#region Constructors
/// <summary>
/// Computes an Eulerian path in the specified digraph, if one exists.
/// </summary>
/// <param name="g">g the digraph</param>
public DirectedEulerianPath(Digraph g)
{
// find vertex from which to start potential Eulerian path:
// a vertex v with outdegree(v) > indegree(v) if it exits;
// otherwise a vertex with outdegree(v) > 0
var deficit = 0;
var s = NonIsolatedVertex(g);
for (var v = 0; v < g.V; v++)
{
if (g.Outdegree(v) > g.Indegree(v))
{
deficit += (g.Outdegree(v) - g.Indegree(v));
s = v;
}
}
// digraph can't have an Eulerian path
// (this condition is needed)
if (deficit > 1) return;
// special case for digraph with zero edges (has a degenerate Eulerian path)
if (s == -1) s = 0;
// create local view of adjacency lists, to iterate one vertex at a time
var adj = new IEnumerator<Integer>[g.V];
for (var v = 0; v < g.V; v++)
adj[v] = g.Adj(v).GetEnumerator();
// greedily add to cycle, depth-first search style
var stack = new Collections.Stack<Integer>();
stack.Push(s);
_path = new Collections.Stack<Integer>();
while (!stack.IsEmpty())
{
int v = stack.Pop();
while (adj[v].MoveNext())
{
stack.Push(v);
v = adj[v].Current;
}
// push vertex with no more available edges to path
_path.Push(v);
}
// check if all edges have been used
if (_path.Size() != g.E + 1)
_path = null;
//assert check(G);
}
/// <summary>
/// Determines whether a digraph has an Eulerian path using necessary
/// and sufficient conditions (without computing the path itself):
/// - indegree(v) = outdegree(v) for every vertex,
/// except one vertex v may have outdegree(v) = indegree(v) + 1
/// (and one vertex v may have indegree(v) = outdegree(v) + 1)
/// - the graph is connected, when viewed as an undirected graph
/// (ignoring isolated vertices)
/// This method is solely for unit testing.
/// </summary>
/// <param name="g"></param>
/// <returns></returns>
private static bool HasEulerianPath(Digraph g)
{
if (g.E == 0)
{
return(true);
}
// Condition 1: indegree(v) == outdegree(v) for every vertex,
// except one vertex may have outdegree(v) = indegree(v) + 1
var deficit = 0;
for (var v = 0; v < g.V; v++)
{
if (g.Outdegree(v) > g.Indegree(v))
{
deficit += (g.Outdegree(v) - g.Indegree(v));
}
}
if (deficit > 1)
{
return(false);
}
// Condition 2: graph is connected, ignoring isolated vertices
var h = new Graph(g.V);
for (var v = 0; v < g.V; v++)
{
foreach (int w in g.Adj(v))
{
h.AddEdge(v, w);
}
}
// check that all non-isolated vertices are connected
var s = NonIsolatedVertex(g);
var bfs = new BreadthFirstPaths(h, s);
for (var v = 0; v < g.V; v++)
{
if (h.Degree(v) > 0 && !bfs.HasPathTo(v))
{
return(false);
}
}
return(true);
}
private readonly Collections.Stack <Integer> _cycle; // Eulerian cycle; null if no such cylce
/// <summary>
/// Computes an Eulerian cycle in the specified digraph, if one exists.
/// </summary>
/// <param name="g">g the digraph</param>
public DirectedEulerianCycle(Digraph g)
{
// must have at least one edge
if (g.E == 0)
{
return;
}
// necessary condition: indegree(v) = outdegree(v) for each vertex v
// (without this check, DFS might return a path instead of a cycle)
for (var v = 0; v < g.V; v++)
{
if (g.Outdegree(v) != g.Indegree(v))
{
return;
}
}
// create local view of adjacency lists, to iterate one vertex at a time
var adj = new IEnumerator <Integer> [g.V];
for (var v = 0; v < g.V; v++)
{
adj[v] = g.Adj(v).GetEnumerator();
}
// initialize stack with any non-isolated vertex
var s = NonIsolatedVertex(g);
var stack = new Collections.Stack <Integer>();
stack.Push(s);
// greedily add to putative cycle, depth-first search style
_cycle = new Collections.Stack <Integer>();
while (!stack.IsEmpty())
{
int v = stack.Pop();
while (adj[v].MoveNext())
{
stack.Push(v);
v = adj[v].Current;
}
// add vertex with no more leaving edges to cycle
_cycle.Push(v);
}
// check if all edges have been used
// (in case there are two or more vertex-disjoint Eulerian cycles)
if (_cycle.Size() != g.E + 1)
{
_cycle = null;
}
//assert certifySolution(G);
}
private readonly int[] _rank; // rank[v] = order where vertex v appers in order
/// <summary>
/// Determines whether the digraph <tt>G</tt> has a topological order and, if so,
/// finds such a topological order.
/// </summary>
/// <param name="g">g the digraph</param>
public TopologicalX(Digraph g)
{
// indegrees of remaining vertices
var indegree = new int[g.V];
for (var v = 0; v < g.V; v++)
{
indegree[v] = g.Indegree(v);
}
// initialize
_rank = new int[g.V];
_order = new Collections.Queue <Integer>();
var count = 0;
// initialize queue to contain all vertices with indegree = 0
var queue = new Collections.Queue <Integer>();
for (var v = 0; v < g.V; v++)
{
if (indegree[v] == 0)
{
queue.Enqueue(v);
}
}
for (var j = 0; !queue.IsEmpty(); j++)
{
int v = queue.Dequeue();
_order.Enqueue(v);
_rank[v] = count++;
foreach (int w in g.Adj(v))
{
indegree[w]--;
if (indegree[w] == 0)
{
queue.Enqueue(w);
}
}
}
// there is a directed cycle in subgraph of vertices with indegree >= 1.
if (count != g.V)
{
_order = null;
}
//assert check(G);
}
/// <summary>
/// Determines whether a digraph has an Eulerian cycle using necessary
/// and sufficient conditions (without computing the cycle itself):
/// - at least one edge
/// - indegree(v) = outdegree(v) for every vertex
/// - the graph is connected, when viewed as an undirected graph
/// (ignoring isolated vertices)
/// </summary>
/// <param name="g"></param>
/// <returns></returns>
private static bool HasEulerianCycle(Digraph g)
{
// Condition 0: at least 1 edge
if (g.E == 0)
{
return(false);
}
// Condition 1: indegree(v) == outdegree(v) for every vertex
for (var v = 0; v < g.V; v++)
{
if (g.Outdegree(v) != g.Indegree(v))
{
return(false);
}
}
// Condition 2: graph is connected, ignoring isolated vertices
var h = new Graph(g.V);
for (var v = 0; v < g.V; v++)
{
foreach (int w in g.Adj(v))
{
h.AddEdge(v, w);
}
}
// check that all non-isolated vertices are conneted
var s = NonIsolatedVertex(g);
var bfs = new BreadthFirstPaths(h, s);
for (var v = 0; v < g.V; v++)
{
if (h.Degree(v) > 0 && !bfs.HasPathTo(v))
{
return(false);
}
}
return(true);
}
/// <summary>
/// Initializes a new digraph that is a deep copy of the specified digraph.
/// </summary>
/// <param name="g">g the digraph to copy</param>
public Digraph(Digraph g) : this(g.V)
{
E = g.E;
for (var v = 0; v < V; v++)
{
_indegree[v] = g.Indegree(v);
}
for (var v = 0; v < g.V; v++)
{
// reverse so that adjacency list is in same order as original
var reverse = new Collections.Stack <Integer>();
foreach (int w in g._adj[v])
{
reverse.Push(w);
}
foreach (int w in reverse)
{
_adj[v].Add(w);
}
}
}
private readonly int[] _rank; // rank[v] = order where vertex v appers in order
#endregion Fields
#region Constructors
/// <summary>
/// Determines whether the digraph <tt>G</tt> has a topological order and, if so,
/// finds such a topological order.
/// </summary>
/// <param name="g">g the digraph</param>
public TopologicalX(Digraph g)
{
// indegrees of remaining vertices
var indegree = new int[g.V];
for (var v = 0; v < g.V; v++)
{
indegree[v] = g.Indegree(v);
}
// initialize
_rank = new int[g.V];
_order = new Collections.Queue<Integer>();
var count = 0;
// initialize queue to contain all vertices with indegree = 0
var queue = new Collections.Queue<Integer>();
for (var v = 0; v < g.V; v++)
if (indegree[v] == 0) queue.Enqueue(v);
for (var j = 0; !queue.IsEmpty(); j++)
{
int v = queue.Dequeue();
_order.Enqueue(v);
_rank[v] = count++;
foreach (int w in g.Adj(v))
{
indegree[w]--;
if (indegree[w] == 0) queue.Enqueue(w);
}
}
// there is a directed cycle in subgraph of vertices with indegree >= 1.
if (count != g.V)
{
_order = null;
}
//assert check(G);
}
/// <summary>
/// Determines whether a digraph has an Eulerian path using necessary
/// and sufficient conditions (without computing the path itself):
/// - indegree(v) = outdegree(v) for every vertex,
/// except one vertex v may have outdegree(v) = indegree(v) + 1
/// (and one vertex v may have indegree(v) = outdegree(v) + 1)
/// - the graph is connected, when viewed as an undirected graph
/// (ignoring isolated vertices)
/// This method is solely for unit testing.
/// </summary>
/// <param name="g"></param>
/// <returns></returns>
private static bool HasEulerianPath(Digraph g)
{
if (g.E == 0) return true;
// Condition 1: indegree(v) == outdegree(v) for every vertex,
// except one vertex may have outdegree(v) = indegree(v) + 1
var deficit = 0;
for (var v = 0; v < g.V; v++)
if (g.Outdegree(v) > g.Indegree(v))
deficit += (g.Outdegree(v) - g.Indegree(v));
if (deficit > 1) return false;
// Condition 2: graph is connected, ignoring isolated vertices
var h = new Graph(g.V);
for (var v = 0; v < g.V; v++)
foreach (int w in g.Adj(v))
h.AddEdge(v, w);
// check that all non-isolated vertices are connected
var s = NonIsolatedVertex(g);
var bfs = new BreadthFirstPaths(h, s);
for (var v = 0; v < g.V; v++)
if (h.Degree(v) > 0 && !bfs.HasPathTo(v))
return false;
return true;
}
private readonly Collections.Stack <Integer> _cycle; // the directed cycle; null if digraph is acyclic
public DirectedCycleX(Digraph g)
{
// indegrees of remaining vertices
var indegree = new int[g.V];
for (var v = 0; v < g.V; v++)
{
indegree[v] = g.Indegree(v);
}
// initialize queue to contain all vertices with indegree = 0
var queue = new Collections.Queue <Integer>();
for (var v = 0; v < g.V; v++)
{
if (indegree[v] == 0)
{
queue.Enqueue(v);
}
}
for (var j = 0; !queue.IsEmpty(); j++)
{
int v = queue.Dequeue();
foreach (int w in g.Adj(v))
{
indegree[w]--;
if (indegree[w] == 0)
{
queue.Enqueue(w);
}
}
}
// there is a directed cycle in subgraph of vertices with indegree >= 1.
var edgeTo = new int[g.V];
var root = -1; // any vertex with indegree >= -1
for (var v = 0; v < g.V; v++)
{
if (indegree[v] == 0)
{
continue;
}
root = v;
foreach (int w in g.Adj(v))
{
if (indegree[w] > 0)
{
edgeTo[w] = v;
}
}
}
if (root != -1)
{
// find any vertex on cycle
var visited = new bool[g.V];
while (!visited[root])
{
visited[root] = true;
root = edgeTo[root];
}
// extract cycle
_cycle = new Collections.Stack <Integer>();
var v = root;
do
{
_cycle.Push(v);
v = edgeTo[v];
} while (v != root);
_cycle.Push(root);
}
//assert check();
}
private readonly Collections.Stack <Integer> _path; // Eulerian path; null if no suh path
/// <summary>
/// Computes an Eulerian path in the specified digraph, if one exists.
/// </summary>
/// <param name="g">g the digraph</param>
public DirectedEulerianPath(Digraph g)
{
// find vertex from which to start potential Eulerian path:
// a vertex v with outdegree(v) > indegree(v) if it exits;
// otherwise a vertex with outdegree(v) > 0
var deficit = 0;
var s = NonIsolatedVertex(g);
for (var v = 0; v < g.V; v++)
{
if (g.Outdegree(v) > g.Indegree(v))
{
deficit += (g.Outdegree(v) - g.Indegree(v));
s = v;
}
}
// digraph can't have an Eulerian path
// (this condition is needed)
if (deficit > 1)
{
return;
}
// special case for digraph with zero edges (has a degenerate Eulerian path)
if (s == -1)
{
s = 0;
}
// create local view of adjacency lists, to iterate one vertex at a time
var adj = new IEnumerator <Integer> [g.V];
for (var v = 0; v < g.V; v++)
{
adj[v] = g.Adj(v).GetEnumerator();
}
// greedily add to cycle, depth-first search style
var stack = new Collections.Stack <Integer>();
stack.Push(s);
_path = new Collections.Stack <Integer>();
while (!stack.IsEmpty())
{
int v = stack.Pop();
while (adj[v].MoveNext())
{
stack.Push(v);
v = adj[v].Current;
}
// push vertex with no more available edges to path
_path.Push(v);
}
// check if all edges have been used
if (_path.Size() != g.E + 1)
{
_path = null;
}
//assert check(G);
}
/// <summary>
/// Initializes a new digraph that is a deep copy of the specified digraph.
/// </summary>
/// <param name="g">g the digraph to copy</param>
public Digraph(Digraph g)
: this(g.V)
{
E = g.E;
for (var v = 0; v < V; v++)
_indegree[v] = g.Indegree(v);
for (var v = 0; v < g.V; v++)
{
// reverse so that adjacency list is in same order as original
var reverse = new Collections.Stack<Integer>();
foreach (int w in g._adj[v])
{
reverse.Push(w);
}
foreach (int w in reverse)
{
_adj[v].Add(w);
}
}
}
private readonly Collections.Stack<Integer> _cycle; // the directed cycle; null if digraph is acyclic
#endregion Fields
#region Constructors
public DirectedCycleX(Digraph g)
{
// indegrees of remaining vertices
var indegree = new int[g.V];
for (var v = 0; v < g.V; v++)
{
indegree[v] = g.Indegree(v);
}
// initialize queue to contain all vertices with indegree = 0
var queue = new Collections.Queue<Integer>();
for (var v = 0; v < g.V; v++)
if (indegree[v] == 0) queue.Enqueue(v);
for (var j = 0; !queue.IsEmpty(); j++)
{
int v = queue.Dequeue();
foreach (int w in g.Adj(v))
{
indegree[w]--;
if (indegree[w] == 0) queue.Enqueue(w);
}
}
// there is a directed cycle in subgraph of vertices with indegree >= 1.
var edgeTo = new int[g.V];
var root = -1; // any vertex with indegree >= -1
for (var v = 0; v < g.V; v++)
{
if (indegree[v] == 0) continue;
root = v;
foreach (int w in g.Adj(v))
{
if (indegree[w] > 0)
{
edgeTo[w] = v;
}
}
}
if (root != -1)
{
// find any vertex on cycle
var visited = new bool[g.V];
while (!visited[root])
{
visited[root] = true;
root = edgeTo[root];
}
// extract cycle
_cycle = new Collections.Stack<Integer>();
var v = root;
do
{
_cycle.Push(v);
v = edgeTo[v];
} while (v != root);
_cycle.Push(root);
}
//assert check();
}