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// Dijkstra's Algorithm in C++
#include <iostream>
#include <vector>
#include <limits.h>
using namespace std;
void DijkstrasTest();
int main() {
DijkstrasTest();
return 0;
}
class Node;
class Edge;
void Dijkstras();
vector<Node*>* AdjacentRemainingNodes(Node* node);
Node* ExtractSmallest(vector<Node*>& nodes);
double Distance(Node* node1, Node* node2);
bool Contains(vector<Node*>& nodes, Node* node);
void PrintShortestRouteTo(Node* destination);
vector<Node*> nodes;
vector<Edge*> edges;
class Node {
public:
Node(char id)
: id(id), previous(NULL), distanceFromStart(INT_MAX) {
nodes.push_back(this);
}
public:
char id;
Node* previous;
double distanceFromStart;
};
class Edge {
public:
Edge(Node* node1, Node* node2, double distance)
: node1(node1), node2(node2), distance(distance) {
edges.push_back(this);
}
bool Connects(Node* node1, Node* node2) {
return (
(node1 == this->node1 &&
node2 == this->node2) ||
(node1 == this->node2 &&
node2 == this->node1));
}
public:
Node* node1;
Node* node2;
double distance;
};
///////////////////
void DijkstrasTest() {
Node* a = new Node('a');
Node* b = new Node('b');
Node* c = new Node('c');
Node* d = new Node('d');
Node* e = new Node('e');
Node* f = new Node('f');
Node* g = new Node('g');
Edge* e1 = new Edge(a, c, 1.74);
Edge* e2 = new Edge(a, d, 2.156);
Edge* e3 = new Edge(b, c, 2.516);
Edge* e4 = new Edge(c, d, 1.321);
Edge* e5 = new Edge(b, f, 3.51);
Edge* e6 = new Edge(c, e, 3.11);
Edge* e7 = new Edge(e, f, 2.2);
Edge* e8 = new Edge(d, g, 1.1);
Edge* e9 = new Edge(g, f, 1.5);
a->distanceFromStart = 0; // set start node
Dijkstras();
PrintShortestRouteTo(f);
}
///////////////////
void Dijkstras() {
while (nodes.size() > 0) {
Node* smallest = ExtractSmallest(nodes);
vector<Node*>* adjacentNodes =
AdjacentRemainingNodes(smallest);
const int size = adjacentNodes->size();
for (int i = 0; i < size; ++i) {
Node* adjacent = adjacentNodes->at(i);
double distance = Distance(smallest, adjacent) +
smallest->distanceFromStart;
if (distance < adjacent->distanceFromStart) {
adjacent->distanceFromStart = distance;
adjacent->previous = smallest;
}
}
delete adjacentNodes;
}
}
// Find the node with the smallest distance,
// remove it, and return it.
Node* ExtractSmallest(vector<Node*>& nodes) {
int size = nodes.size();
if (size == 0) return NULL;
int smallestPosition = 0;
Node* smallest = nodes.at(0);
for (int i = 1; i < size; ++i) {
Node* current = nodes.at(i);
if (current->distanceFromStart <
smallest->distanceFromStart) {
smallest = current;
smallestPosition = i;
}
}
nodes.erase(nodes.begin() + smallestPosition);
return smallest;
}
// Return all nodes adjacent to 'node' which are still
// in the 'nodes' collection.
vector<Node*>* AdjacentRemainingNodes(Node* node) {
vector<Node*>* adjacentNodes = new vector<Node*>();
const int size = edges.size();
for (int i = 0; i < size; ++i) {
Edge* edge = edges.at(i);
Node* adjacent = NULL;
if (edge->node1 == node) {
adjacent = edge->node2;
} else if (edge->node2 == node) {
adjacent = edge->node1;
}
if (adjacent && Contains(nodes, adjacent)) {
adjacentNodes->push_back(adjacent);
}
}
return adjacentNodes;
}
// Return distance between two connected nodes
double Distance(Node* node1, Node* node2) {
const int size = edges.size();
for (int i = 0; i < size; ++i) {
Edge* edge = edges.at(i);
if (edge->Connects(node1, node2)) {
return edge->distance;
}
}
return -1; // should never happen
}
// Does the 'nodes' vector contain 'node'
bool Contains(vector<Node*>& nodes, Node* node) {
const int size = nodes.size();
for (int i = 0; i < size; ++i) {
if (node == nodes.at(i)) {
return true;
}
}
return false;
}
///////////////////
void PrintShortestRouteTo(Node* destination) {
Node* previous = destination;
cout << "Distance from start: "
<< destination->distanceFromStart << endl;
while (previous) {
cout << previous->id << " ";
previous = previous->previous;
}
cout << endl;
}
// these two not needed
vector<Edge*>* AdjacentEdges(vector<Edge*>& Edges, Node* node);
void RemoveEdge(vector<Edge*>& Edges, Edge* edge);
vector<Edge*>* AdjacentEdges(vector<Edge*>& edges, Node* node) {
vector<Edge*>* adjacentEdges = new vector<Edge*>();
const int size = edges.size();
for (int i = 0; i < size; ++i) {
Edge* edge = edges.at(i);
if (edge->node1 == node) {
cout << "adjacent: " << edge->node2->id << endl;
adjacentEdges->push_back(edge);
} else if (edge->node2 == node) {
cout << "adjacent: " << edge->node1->id << endl;
adjacentEdges->push_back(edge);
}
}
return adjacentEdges;
}
void RemoveEdge(vector<Edge*>& edges, Edge* edge) {
vector<Edge*>::iterator it;
for (it = edges.begin(); it < edges.end(); ++it) {
if (*it == edge) {
edges.erase(it);
return;
}
}
}
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