Djikstra's Algorithm in C++ - algorithm

Question

I am writing Djikstra's algorithm in C++, and am having trouble getting the code to print anything other than the path from A->A. I need to get it to find the path from A->X where X is any one of the nodes A-I.
Expected Output
Actual Output
#include <climits>
#include <fstream>
#include <iostream>
using namespace std;
const int V = 9;
// Function to print shortest path from source to j
// using parent array
void printPath(int parent[], int j) {
char str = j;
// Base Case : If j is source
if (parent[j] == -1) {
cout << str << " ";
return;
}
printPath(parent, parent[j]);
// printf("%d ", j);
cout << str << " ";
}
int miniDist(int distance[], bool Tset[]) // finding minimum distance
{
int minimum = INT_MAX, ind;
for (int k = 0; k < V; k++) {
if (Tset[k] == false && distance[k] <= minimum) {
minimum = distance[k];
ind = k;
}
}
return ind;
}
void DijkstraAlgo(int graph[V][V], char sourceNode,
char endNode) // adjacency matrix
{
int distance[V]; // array to calculate the minimum distance for each node
bool Tset[V]; // boolean array to mark visited and unvisited for each node
int parent[V]; // Parent array to store shortest path tree
// Value of parent[v] for a vertex v stores parent vertex of v
// in shortest path tree.
for (int k = 0; k < V; k++) {
distance[k] = INT_MAX;
Tset[k] = false;
}
parent[sourceNode] = -1; // Parent of root (or source vertex) is -1.
distance[sourceNode] = 0; // Source vertex distance is set 0
for (int k = 0; k < V; k++) {
int end = miniDist(distance, Tset);
Tset[end] = true;
for (int k = 0; k < V; k++) {
// updating the distance of neighbouring vertex
if (!Tset[k] && graph[end][k] && distance[end] != INT_MAX &&
distance[end] + graph[end][k] < distance[k]) {
distance[k] = distance[end] + graph[end][k];
parent[k] = end;
}
}
}
cout << "Vertex\t\tDistance from source vertex\t\t Path" << endl;
int k = sourceNode;
char str = k;
// cout<<str<<"\t\t\t"<<distance[k]<<endl;
cout << str << "\t\t\t" << distance[k] << "\t\t\t\t\t\t\t\t";
printPath(parent, k);
cout << endl;
}
int main() {
char choice1, choice2;
ifstream inFile;
inFile.open("graph.txt");
int graph[V][V];
for (int i = 0; i < V; i++) {
for (int j = 0; j < V; j++)
inFile >> graph[i][j];
}
cout << "Nodes: "
<< "A, B, C, D, E, F, G, H, I" << endl;
cout << "Enter starting node: ";
cin >> choice1;
cout << "Enter ending node: ";
cin >> choice2;
cout << endl;
DijkstraAlgo(graph, choice1, choice2);
inFile.close();
return 0;
}
So, I have to be able to pass the endNode parameter to something somehow, correct?

Answer 1

The main issue lies here:
int miniDist(int distance[], bool Tset[])
In your minimum distance calculation, you don't exclude the source vertex. All other vertices have INT_MAX distance and the source has 0 distance, so it gets picked. Try going through the algorithm once again to fix your implementation.