在过去的一周中,我通过解析输入文件来实现了有向图。该图保证没有循环。我成功地创建了图形,使用方法返回了顶点和边的数量,并对图形执行了拓扑排序。该图由不同的主要课程及其先决条件组成。这是我的图形设置:
该实现
class vertex{
public:
typedef std::pair<int, vertex*> ve;
std::vector<ve> adjacency;
std::string course;
vertex(std::string c){
course = c;
}
};
class Digraph{
public:
typedef std::map<std::string, vertex *> vmap;
vmap work;
typedef std::unordered_set<vertex*> marksSet;
marksSet marks;
typedef std::deque<vertex*> stack;
stack topo;
void dfs(vertex* vcur);
void addVertex(std::string&);
void addEdge(std::string& from, std::string& to, int cost);
int getNumVertices();
int getNumEdges();
void getTopoSort();
};
该实现
//function to add vertex's to the graph
void Digraph::addVertex(std::string& course){
vmap::iterator iter = work.begin();
iter = work.find(course);
if(iter == work.end()){
vertex *v;
v = new vertex(course);
work[course] = v;
return;
}
}
//method to add edges to the graph
void Digraph::addEdge(std::string& from, std::string& to, int cost){
vertex *f = (work.find(from)->second);
vertex *t = (work.find(to)->second);
std::pair<int, vertex *> edge = std::make_pair(cost, t);
f->adjacency.push_back(edge);
}
//method to return the number of vertices in the graph
int Digraph::getNumVertices(){
return work.size();
}
//method to return the number of edges in the graph
int Digraph::getNumEdges(){
int count = 0;
for (const auto & v : work) {
count += v.second->adjacency.size();
}
return count;
}
//recursive function used by the topological sort method
void Digraph::dfs(vertex* vcur) {
marks.insert(vcur);
for (const auto & adj : vcur->adjacency) {
vertex* suc = adj.second;
if (marks.find(suc) == marks.end()) {
this->dfs(suc);
}
}
topo.push_front(vcur);
}
//method to calculate and print out a topological sort of the graph
void Digraph::getTopoSort(){
marks.clear();
topo.clear();
for (const auto & v : work) {
if (marks.find(v.second) == marks.end()) {
this->dfs(v.second);
}
}
// Display it
for (const auto v : topo) {
std::cout << v->course << "\n";
}
}
在我的实现的最后一部分,我一直在尝试做两件事。找到从第一个顶点到每个其他顶点的最短路径,以及找到访问每个顶点并返回第一个顶点的最短路径。我对这个实现完全感到迷失。我从阅读中假设需要使用Dijkstra算法来实现这一点。我已经尝试了最近3天,但无济于事。我是否设置了错误的有向图来实现这些步骤?任何指导都将不胜感激。