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complete AStar & Dijkstra #3

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64 changes: 64 additions & 0 deletions AStar.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -28,8 +28,11 @@
#include <limits>
#include <utility> // for pair
#include <stack> // for reconstructing the path
#include <unordered_set>
#include <unordered_map>

using namespace std;
#define INF 1e9

// Graph representation using adjacency list
class Graph {
Expand Down Expand Up @@ -60,15 +63,76 @@ class Graph {
// Your implementation goes here

// 1. Create a priority queue for vertices being processed
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> openSet; //pair<distance, city>
unordered_set<int> closedSet;

// 2. Create arrays for g_score (actual distance from start)
// and f_score (g_score + heuristic)
// 3. Initialize all g_scores as INFINITE and src g_score as 0
vector<int> gScore(V, INF);
vector<int> fScore(V, INF);
vector<int> from(V, -1);

gScore[src] = 0;
fScore[src] = heuristic[src];
openSet.push({fScore[src], src});
// 4. Process vertices in order of their f_score (not just distance)
while(!openSet.empty())
{
int current = openSet.top().second;
int currentfScore = openSet.top().first;
openSet.pop();

if(fScore[current] < currentfScore) continue;
if(current == dest) break;
closedSet.insert(current);

for(auto& edge : adj[current])
{
int next = edge.first;
int weight = edge.second;

int gNext = gScore[current] + weight;
if(gNext < gScore[next])
{
gScore[next] = gNext;
fScore[next] = gScore[next] + heuristic[next];
from[next] = current;
// if(closedSet.find(next) == closedSet.end())
// {
openSet.push({fScore[next], next});
// }
}
}
}
// 5. Reconstruct and print the shortest path from src to dest
if(gScore[dest] == INF) cout << "No path exists from " << src << " to " << dest << endl;
else
{
stack<int> path;
cout << "Shortest travel time: " << gScore[dest] << " hours" << endl;
cout << "Shortest travel time: " << fScore[dest] << " hours" << endl;
cout << "Shortest path from " << src << " to " << dest << ": ";
int current = dest;
while(current != -1)
{
path.push(current);
current = from[current];
}
while(!path.empty())
{
cout << path.top() << '(' << gScore[path.top()] << ')';
path.pop();
if(!path.empty()) cout << " -> ";
}
cout << endl;
}
}
};

int main() {
std::ios::sync_with_stdio(false);
std::cin.tie(0);
// Create graph with 6 cities (labeled 0 to 5)
Graph g(6);

Expand Down
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81 changes: 71 additions & 10 deletions Dijkstra.cpp
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Expand Up @@ -27,6 +27,8 @@
#include <utility> // for pair
#include <stack> // for reconstructing the path

#define INF 1e9

using namespace std;

// Graph representation using adjacency list
Expand All @@ -51,26 +53,85 @@ class Graph {
// Your implementation goes here

// 1. Create a priority queue for vertices being processed
priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> q; //pair<distance, city>
// 2. Create arrays for distances and for tracking the path
// 3. Initialize all distances as INFINITE and src distance as 0
vector<int> dist(V, INF);
vector<int> prev(V, -1);
dist[src] = 0;
q.push({0, src});
// 4. Process vertices in order of their distance from src
while(!q.empty())
{
int current = q.top().second;
q.pop();

if(current == dest) break;

for(auto& edge : adj[current])
{
int next = edge.first;
int weight = edge.second;
if(dist[next] > dist[current] + weight)
{
dist[next] = dist[current] + weight;
prev[next] = current;
q.push({dist[next], next});
}
}
}
// 5. Reconstruct and print the shortest path from src to dest
if(dist[dest] == INF) cout << "No path exists from " << src << " to " << dest << endl;
else
{
stack<int> path;
int current = dest;
while(current != -1)
{
path.push(current);
current = prev[current];
}
cout << "Shortest travel time: " << dist[dest] << " hours" << endl;
cout << "Path: ";
while(!path.empty())
{
cout << path.top();
path.pop();
if(!path.empty()) cout << " -> ";
}
cout << endl;
}
}
};

int main() {

int n;
cout << "Enter the number of cities: " << endl;
cin >> n;
// Create graph with 6 cities (labeled 0 to 5)
Graph g(6);
Graph g(n);

// Add roads with travel times (directed edges with weights)
g.addEdge(0, 1, 2); // From city 0 to city 1, travel time: 2 hours
g.addEdge(0, 2, 4); // From city 0 to city 2, travel time: 4 hours
g.addEdge(1, 2, 1); // From city 1 to city 2, travel time: 1 hour
g.addEdge(1, 3, 7); // From city 1 to city 3, travel time: 7 hours
g.addEdge(2, 4, 3); // From city 2 to city 4, travel time: 3 hours
g.addEdge(3, 5, 1); // From city 3 to city 5, travel time: 1 hour
g.addEdge(4, 3, 2); // From city 4 to city 3, travel time: 2 hours
g.addEdge(4, 5, 5); // From city 4 to city 5, travel time: 5 hours
// g.addEdge(0, 1, 2); // From city 0 to city 1, travel time: 2 hours
// g.addEdge(0, 2, 4); // From city 0 to city 2, travel time: 4 hours
// g.addEdge(1, 2, 1); // From city 1 to city 2, travel time: 1 hour
// g.addEdge(1, 3, 7); // From city 1 to city 3, travel time: 7 hours
// g.addEdge(2, 4, 3); // From city 2 to city 4, travel time: 3 hours
// g.addEdge(3, 5, 1); // From city 3 to city 5, travel time: 1 hour
// g.addEdge(4, 3, 2); // From city 4 to city 3, travel time: 2 hours
// g.addEdge(4, 5, 5); // From city 4 to city 5, travel time: 5 hours

int u, v, w;
cout << "Enter the edges: (u, v, w) , input u as -1 to exit" << endl;
while(true)
{
cin >> u;
if(u == -1) break;
cin >> v >> w;

g.addEdge(u, v, w);
}

// Find the shortest path from city 0 (start) to city 5 (destination)
cout << "Shortest path from city 0 to city 5:" << endl;
Expand All @@ -94,5 +155,5 @@ int main() {
*
* Optional challenge:
* - Modify the implementation to handle different start and destination cities as user input
* - Visualize the graph and the shortest path
* - Visualize the graph and the shortest path
*/
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