Advanced algorithms strongly connected components algorithm s, Euler trail , Hamiltonian path

Advanced algorithms strongly connected components algorithms, Euler trail, Hamiltonian path Jiří Vyskočil, Radek Mařík 2013

Connected component b C(a)=C(b)={a,b} c a C(c) =C(d) =C(e)={c,d,e} d e A connected component of graphG =(V,E ) with regard to vertex vis a set C(v ) = {u∈V | there exists a pathin G fromutov }. In other words: If a graph is disconnected, then parts from which is composed from and that are themselves connected, are called connected components.

Strongly Connected Components[silně souvislé komponenty] a b c d e f g h A directed graph G =(V,E )is called strongly connected if there is a path in each direction between every couple of vertices in the graph. The strongly connected components of a directed graph G are its maximal strongly connected subgraphs. SCC(v ) = {u∈V | there exists a pathin G fromutov and a pathin G fromvtou}

Kosaraju-SharirAlgorithm input: graph G = (V, E ) output: set of strongly connected components (sets of vertices) • S = empty stack; • whileS does not contain all vertices do Choose an arbitrary vertex v not in S; DFS-Walk’(v ) and each time that DFS finishes expanding a vertex u, push u onto S; • Reverse the directions of all arcs to obtain the transpose graph; • whileS is nonempty do v = pop(S); ifv is UNVISITED then DFS-Walk(v ); The set of visited vertices will give the strongly connected component containing v;

DFS-Walk • input:Graph G. • procedure DFS-Walk(Vertex u ) { • state[u ] = OPEN; d[u ] = ++time; • for each Vertexvin succ(u ) • if (state[v ] == UNVISITED) then{p[v ] = u; DFS-Walk(v ); } • state[u ] = CLOSED; f[u ] = ++time; • } • procedure DFS-Walk’(Vertex u ) { • state[u ] = OPEN; d[u ] = ++time; • for each Vertexvin succ(u ) • if (state[v ] == UNVISITED) then{p[v ] = u; DFS-Walk’(v ); } • state[u ] = CLOSED; f[u ] = ++time; push u to S; • } • output: arrayppointing to predecessor vertex, array dwith times of vertex opening and array fwith time of vertex closing.

DFS-Walk - optimized • input:Graph G. • procedure DFS-Walk(Vertex u ) { • state[u ] = OPEN; • for each Vertexvin succ(u ) • if (state[v ] == UNVISITED) thenDFS-Walk(v ); • state[u ] = CLOSED; • } • procedure DFS-Walk’(Vertex u ) { • state[u ] = OPEN; • for each Vertexvin succ(u ) • if (state[v ] == UNVISITED) thenDFS-Walk’(v ); • state[u ] = CLOSED; push u to S; • }

Kosaraju-SharirAlgorithm a b c d e f g h OPEN CLOSED UNVISITED

Advanced algorithms strongly connected components algorithm s, Euler trail , Hamiltonian path

Advanced algorithms strongly connected components algorithm s, Euler trail , Hamiltonian path

Presentation Transcript

Augmenting Path Algorithm

Shortest Path Algorithm

Find Strongly Connected C omponents Using K osaraju’s Algorithm And T arjan’s Algorithm

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Shortest Path Algorithm

Strongly quasi-Hamiltonian-connected multipartite tournament

BBG2 Algorithm s Components of an Algorithm

Data Structures – LECTURE 14 Strongly connected components

Shortest Path Algorithm

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Hw. 6: Algorithm for finding strongly connected components.

Data Structures – LECTURE 14 Strongly connected components

Shortest Path Algorithm

Shortest Path Algorithm

Euler and Hamiltonian Graphs

Euler and Hamiltonian Graphs

Strongly Connected Components for Directed Graphs

Shortest Path Algorithm