C16 Megan Hagar

lib/dijkstra.py

@@ -1,3 +1,32 @@
-
 def dijkstra(adjacency_matrix, start_node):
-    pass
+    parent_list = [None]*len(adjacency_matrix)
+    shortest_distances = [float('inf')]*len(adjacency_matrix)
+
+    traversal_queue = [start_node]
+    visited_nodes = set()
+    shortest_distances[start_node] = 0
+
+    while traversal_queue:
+        current_node = traversal_queue.pop(0) 
+
+        # check if we looked at this node's adjacency list yet, if we have, skip
+        if current_node in visited_nodes:
+            continue
+
+        visited_nodes.add(current_node)
+
+        # iterate through the current nodes adjacency matrix
+        for node, cost in enumerate(adjacency_matrix[current_node]): 
+            # if there is a relationship to another node, add it to queue
+            if cost != 0:
+                traversal_queue.append(node)
+
+                # calculate the distance from current node to each additional connection
+                # if the distance is less than shortest distance to that node already, or 
+                # there is no recorded distance to that node, update distance list, and parent list
+                current_distance = cost + shortest_distances[current_node] 
+                if shortest_distances[node] == float('inf') or shortest_distances[node] > current_distance:
+                    parent_list[node] = current_node 
+                    shortest_distances[node] = current_distance
+
+    return {"start_node": start_node, "parent_list": parent_list, "shortest_distances": shortest_distances}