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https://github.com/onyx-and-iris/grokking-algorithms.git
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56 lines
1.4 KiB
Python
56 lines
1.4 KiB
Python
import heapq
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import logging
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import math
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logging.basicConfig(level=logging.DEBUG)
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logger = logging.getLogger(__name__)
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graph = {
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"start": {"a": 5, "b": 2},
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"a": {"b": 8, "c": 4, "d": 2},
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"b": {"a": 8, "d": 7},
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"c": {"d": 6, "fin": 3},
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"d": {"fin": 1},
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"fin": {},
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}
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def dijkstra(graph, node):
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costs = {node: math.inf for node in graph}
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costs[node] = 0
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parents = {node: None for node in graph}
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queue = [(0, node)]
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while queue:
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current_cost, current_node = heapq.heappop(queue)
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logger.debug(f"node {current_node} with cost {current_cost} popped from pqueue")
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for next_node, weight in graph[current_node].items():
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new_cost = current_cost + weight
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if new_cost < costs[next_node]:
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costs[next_node] = new_cost
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parents[next_node] = current_node
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heapq.heappush(queue, (new_cost, next_node))
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logger.debug(
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f"node {next_node} with new cost {new_cost} appended to pqueue"
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)
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return costs, parents
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costs, parents = dijkstra(graph, "start")
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print(f"lowest cost from start to fin: {costs['fin']}")
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def get_full_route():
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route = []
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next = "fin"
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while next != "start":
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route.append(next)
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next = parents[next]
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route.append("start")
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return list(reversed(route))
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print(f"full route: {get_full_route()}")
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