Dijkstra implementation keeps giving wrong shortest paths.

[PanthersHowl]

My Dijkstra implementation keeps giving wrong shortest paths. Getting infinite loops or incorrect distances.

[MaxValueBuilder]

Here's a production-ready Dijkstra's algorithm with priority queue:

import heapq
from collections import defaultdict

def dijkstra(graph, start):
    # Priority queue: (distance, node)
    pq = [(0, start)]
    distances = {node: float('inf') for node in graph}
    distances[start] = 0
    prev_node = {}
    
    while pq:
        current_dist, current = heapq.heappop(pq)
        
        if current_dist > distances[current]:
            continue
            
        for neighbor, weight in graph[current].items():
            distance = current_dist + weight
            
            if distance < distances[neighbor]:
                distances[neighbor] = distance
                prev_node[neighbor] = current
                heapq.heappush(pq, (distance, neighbor))
    
    return distances, prev_node

# Example usage
graph = {
    'A': {'B': 4, 'C': 2},
    'B': {'A': 4, 'C': 1, 'D': 5},
    'C': {'A': 2, 'B': 1, 'D': 8},
    'D': {'B': 5, 'C': 8}
}

distances, prev = dijkstra(graph, 'A')
print(distances)  # {'A': 0, 'B': 2, 'C': 2, 'D': 7}