[英]Dijkstra's algorithm - adjacency matrix and list
I've got strange problem with my Dijkstra's implementation... I have 2 algorithms, one for adjacency matrix and the second one for adjacency list. 我的Dijkstra的实现遇到了一个奇怪的问题……我有2种算法,一种算法用于邻接矩阵,第二种算法用于邻接表。 They are almost identical and only difference is with passing numbers from these structures.
它们几乎是相同的,唯一的区别是这些结构传递的数字。
I keep numbers from matrix in simple two-dimensional matrix called weightmat. 我将矩阵中的数字保留在称为weightmat的简单二维矩阵中。 Numbers from list are kept in array of lists called nbhlist.
列表中的数字保存在称为nbhlist的列表数组中。 Lists are composed from structs called ListNode.
列表由称为ListNode的结构组成。
struct ListNode{
int number;
int weight;
ListNode* next;
ListNode(){
number = weight = 0;
next = 0;
}
};
And few general variables: vertex (number of vertices), edge (number of edges), vstart (number of start vertex). 很少有一般变量:顶点(顶点数),边(边数),vstart(起始顶点数)。
Now code of Dijkstra's algorithm for matrix: 现在,Dijkstra的矩阵算法代码:
typedef vector<vector<pair<int, float> > > Graph;
struct Compare{
int operator() (const pair<int,float>& p1, const pair<int,float>& p2)
{
return p1.second > p2.second;
}
};
vector<float> d(vertex);
vector<int> parent(vertex);
for (int i = 0; i < vertex; i++){
d[i] = numeric_limits<float>::max();
parent[i] = -1;
}
priority_queue<pair<int, float>, vector<pair<int, float> >, Compare> MatQueue;
d[vstart] = 0;
MatQueue.push(make_pair(vstart, d[vstart]));
while (!MatQueue.empty()){
int u = MatQueue.top().first;
if (u == vertex - 1) break;
MatQueue.pop();
for (int i = 0; i < vertex; i++){
if (weightmat[u][i] != 0){
int v = i;
float w = weightmat[u][i];
//cout << "U " << u << "Number " << i << " Weight " << weightmat[u][i] << endl;
if (d[v]> d[u] + w){
d[v] = d[u] + w;
parent[v] = u;
MatQueue.push(make_pair(v, d[v]));
}
}
}
}
vector<int> path;
path.clear();
int p = vertex - 1;
path.push_back(vertex - 1);
while (p != vstart)
{
p = parent[p];
path.push_back(p);
}
for (int i = path.size()-1; i >=0; i--){
cout << path[i] << "->";
}
And this is code of Dijkstra's algorithm for my lists: 这是Dijkstra的算法代码列表:
typedef vector<vector<pair<int, float> > > Graph;
struct Compare{
int operator() (const pair<int, float>& p1, const pair<int, float>& p2)
{
return p1.second > p2.second;
}
};
vector<float> d(vertex);
vector<int> parent(vertex);
for (int i = 0; i < vertex; i++){
d[i] = numeric_limits<float>::max();
parent[i] = -1;
}
priority_queue<pair<int, float>, vector<pair<int, float> >, Compare> MatQueue;
d[vstart] = 0;
MatQueue.push(make_pair(vstart, d[vstart]));
ListNode* hand = new ListNode;
while (!MatQueue.empty()){
int u = MatQueue.top().first;
if (u == vertex - 1) break;
MatQueue.pop();
hand = NbhList[u];
while (hand){
int v = hand->number;
float w = hand->weight;
//cout << "U " << u << "Number " << v << " Weight " << w << endl;
hand = hand->next;
if (d[v] > d[u] + w){
d[v] = d[u] + w;
parent[v] = u;
MatQueue.push(make_pair(v, d[v]));
}
}
}
vector<int> path;
path.clear();
int p = (vertex-1);
path.push_back(p);
while (p != vstart)
{
p = parent[p];
path.push_back(p);
}
cout << endl << endl;
for (int i = path.size() - 1; i >= 0; i--){
cout << path[i] << "->";
}
As I said, they are almost identical. 正如我所说,它们几乎是相同的。 Only difference:
唯一的区别:
MatQueue.pop();
hand = NbhList[u];
while (hand){
int v = hand->number;
float w = hand->weight;
//cout << "U " << u << "Number " << v << " Weight " << w << endl;
hand = hand->next;
if (d[v] > d[u] + w){
d[v] = d[u] + w;
parent[v] = u;
MatQueue.push(make_pair(v, d[v]));
}
}
And: 和:
MatQueue.pop();
for (int i = 0; i < vertex; i++){
if (weightmat[u][i] != 0){
int v = i;
float w = weightmat[u][i];
//cout << "U " << u << "Number " << i << " Weight " << weightmat[u][i] << endl;
if (d[v]> d[u] + w){
d[v] = d[u] + w;
parent[v] = u;
MatQueue.push(make_pair(v, d[v]));
}
}
}
My problem is - they give me sometimes different outputs and I have no idea why. 我的问题是-它们有时给我不同的输出,我不知道为什么。 Could you help me find my problem?
你能帮我找到我的问题吗?
One possible bug is that in your ListNode
struct: 一个可能的错误是在
ListNode
结构中:
struct ListNode{
int number;
int weight;
ListNode* next;
ListNode(){
number = weight = 0;
next = 0;
}
};
weight
is an int
, but your weights are float
s according to the rest of your code, which might result in unwanted truncation. weight
是一个int
,但根据代码的其余部分,权重为float
,这可能会导致不必要的截断。
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