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# Doing a practice implementation of Dijkstra's algorithm: a priority-first
# search.
from heapq import heappush, heappop
class Node(object):
def __init__(self, value, children):
self.value = value
self.children = children
def shortest_path(a, b):
"""Return the shortest path from `a` to `b`."""
q = []
seen = set()
heappush((a.value, a, [a]), q)
while q:
d, node, path = heappop(q)
if node == b:
return path
seen.add(node)
for child in node.children:
if child not in seen:
heappush((d + child.value, child, path + [child]), q)
raise Exception("Path between nodes A and B does not exist.")
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