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.

1 files changed, 26 insertions, 0 deletions

diff --git a/deepmind/dijkstra.py b/deepmind/dijkstra.py
new file mode 100644
index 000000000000..6975dbe4d1d6
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+++ b/deepmind/dijkstra.py
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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.")