From c010e6d6cff1e348645c337b1c63f8d66a6d6859 Mon Sep 17 00:00:00 2001 From: William Carroll Date: Wed, 22 Jan 2020 11:07:07 +0000 Subject: [PATCH] Practice dijkstra's algorithm Getting some practice with Python's heapq module (which I'm unsure if I used correctly) to do a priority-first-traversal of a graph: known as Dijkstra's algorithm. --- deepmind/dijkstra.py | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) create mode 100644 deepmind/dijkstra.py diff --git a/deepmind/dijkstra.py b/deepmind/dijkstra.py new file mode 100644 index 000000000..6975dbe4d --- /dev/null +++ b/deepmind/dijkstra.py @@ -0,0 +1,26 @@ +# 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.")