making dijkstra_2 better

Author: yashwanth-adimulam

graphs/dijkstra_2.py

@@ -1,58 +1,100 @@
-def print_dist(dist, v):
-    print("\nVertex Distance")
-    for i in range(v):
-        if dist[i] != float("inf"):
-            print(i, "\t", int(dist[i]), end="\t")
-        else:
-            print(i, "\t", "INF", end="\t")
-        print()
+from typing import List
 
+def print_distances(distances: List[float]) -> None:
+    print("\nVertex Distance")
+    for vertex, distance in enumerate(distances):
+        print(f"{vertex}\t{int(distance) if distance != float('inf') else 'INF'}")
 
-def min_dist(mdist, vset, v):
-    min_val = float("inf")
-    min_ind = -1
-    for i in range(v):
-        if (not vset[i]) and mdist[i] < min_val:
-            min_ind = i
-            min_val = mdist[i]
-    return min_ind
+def find_min_distance(distances: List[float], visited: List[bool]) -> int:
+    min_distance = float("inf")
+    min_index = -1
+    
+    for i in range(len(distances)):
+        if not visited[i] and distances[i] < min_distance:
+            min_distance = distances[i]
+            min_index = i
+            
+    return min_index
 
+def dijkstra(graph: List[List[float]], num_vertices: int, source: int) -> List[float]:
+    distances = [float("inf")] * num_vertices
+    visited = [False] * num_vertices
+    distances[source] = 0
 
-def dijkstra(graph, v, src):
-    mdist = [float("inf") for _ in range(v)]
-    vset = [False for _ in range(v)]
-    mdist[src] = 0.0
+    for _ in range(num_vertices - 1):
+        u = find_min_distance(distances, visited)
+        visited[u] = True
 
-    for _ in range(v - 1):
-        u = min_dist(mdist, vset, v)
-        vset[u] = True
+        for v in range(num_vertices):
+            if (not visited[v] and graph[u][v] != float("inf")
+                and distances[u] + graph[u][v] < distances[v]):
+                distances[v] = distances[u] + graph[u][v]
 
-        for i in range(v):
-            if (
-                (not vset[i])
-                and graph[u][i] != float("inf")
-                and mdist[u] + graph[u][i] < mdist[i]
-            ):
-                mdist[i] = mdist[u] + graph[u][i]
+    return distances
 
-    print_dist(mdist, i)
+def is_connected(graph: List[List[float]], num_vertices: int) -> bool:
+    visited = [False] * num_vertices
+    stack = [0]  # Start DFS from the first vertex
+    visited[0] = True
+    
+    while stack:
+        node = stack.pop()
+        for neighbor in range(num_vertices):
+            if graph[node][neighbor] != float("inf") and not visited[neighbor]:
+                visited[neighbor] = True
+                stack.append(neighbor)
 
+    return all(visited)
 
-if __name__ == "__main__":
+def main() -> None:
     V = int(input("Enter number of vertices: ").strip())
-    E = int(input("Enter number of edges: ").strip())
-
-    graph = [[float("inf") for i in range(V)] for j in range(V)]
-
+    if V <= 0:
+        print("Error: The number of vertices must be greater than 0.")
+        return
+    
+    E = int(input("Enter number of edges (must be >= V-1): ").strip())
+    if E < V - 1:
+        print(f"Error: The number of edges must be at least {V - 1} for a connected graph.")
+        return
+    
+    graph = [[float("inf")] * V for _ in range(V)]
+    
     for i in range(V):
         graph[i][i] = 0.0
 
     for i in range(E):
-        print("\nEdge ", i + 1)
-        src = int(input("Enter source:").strip())
-        dst = int(input("Enter destination:").strip())
-        weight = float(input("Enter weight:").strip())
+        print(f"\nEdge {i + 1}")
+        src = int(input(f"Enter source (0 to {V - 1}): ").strip())
+        dst = int(input(f"Enter destination (0 to {V - 1}): ").strip())
+        
+        if src < 0 or src >= V or dst < 0 or dst >= V:
+            print("Error: Source and destination must be valid vertex indices.")
+            return
+        
+        weight = float(input("Enter weight (non-negative): ").strip())
+        if weight < 0:
+            print("Error: Weight must be non-negative.")
+            return
+        
+        if src == dst:
+            print("Warning: Self-loop detected; it will be allowed but consider its implications.")
+
+        # Handle duplicate edges: (optionally overwrite or warn)
+        if graph[src][dst] != float("inf"):
+            print("Warning: Duplicate edge detected; the weight will be updated.")
+
         graph[src][dst] = weight
 
-    gsrc = int(input("\nEnter shortest path source:").strip())
-    dijkstra(graph, V, gsrc)
+    if not is_connected(graph, V):
+        print("Warning: The graph is not connected. Dijkstra's algorithm may not yield valid results for all vertices.")
+
+    gsrc = int(input(f"\nEnter shortest path source (0 to {V - 1}): ").strip())
+    if gsrc < 0 or gsrc >= V:
+        print("Error: Source must be a valid vertex index.")
+        return
+
+    distances = dijkstra(graph, V, gsrc)
+    print_distances(distances)
+
+if __name__ == "__main__":
+    main()