dijkstra in python

Here's an implementation of Dijkstra's algorithm in Python:

import heapq

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

To use this function, you'll need to represent your graph as a dictionary of dictionaries. Each key in the outer dictionary represents a node in the graph, and its value is another dictionary that maps the node's neighbors to their edge weights. For example:

graph = {
    'A': {'B': 2, 'C': 1},
    'B': {'A': 2, 'D': 4},
    'C': {'A': 1, 'D': 3},
    'D': {'B': 4, 'C': 3}
}

print(dijkstra(graph, 'A'))
# Output: {'A': 0, 'B': 2, 'C': 1, 'D': 4}

This code will find the shortest path from the start node ('A') to every other node in the graph. The output is a dictionary that maps each node to its shortest distance from the start node.