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perf: path_BFS, path_UCS and path_Astar no longer scan lists #54

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Merged
petercorke merged 2 commits into from
Oct 12, 2026
Merged

perf: path_BFS, path_UCS and path_Astar no longer scan lists #54

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0c0f013
perf: path_BFS, path_UCS and path_Astar no longer scan lists
petercorke Oct 12, 2026
e1c3db2
Merge branch 'main' into perf/path-planners
petercorke Oct 12, 2026
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63 changes: 45 additions & 18 deletions src/pgraph/PGraph.py
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,8 @@
from matplotlib.transforms import Affine2D, ScaledTranslation
from mpl_toolkits.mplot3d import proj3d
import copy
import heapq
from collections import deque
from collections.abc import Iterable, Iterator
import tempfile
import webbrowser
Expand Down Expand Up @@ -3074,7 +3076,10 @@ def path_BFS(

# we use lists not sets since the order is instructive in verbose
# mode, really need ordered sets...
frontier: list[Vertex] = [S]
# the frontier is a queue; ``seen`` is everything that has been on it,
# so that "frontier or explored" is a set lookup, not a list scan
frontier: deque[Vertex] = deque([S])
seen: set[Vertex] = {S}
explored: list[Vertex] = []
parent: dict[Vertex, Vertex] = {}
done = False
Expand All @@ -3085,7 +3090,7 @@ def path_BFS(
print("FRONTIER:", ", ".join([str(v.name) for v in frontier]))
print("EXPLORED:", ", ".join([str(v.name) for v in explored]))

x = frontier.pop(0)
x = frontier.popleft()
if verbose:
print(" expand", x.name)

Expand All @@ -3099,8 +3104,9 @@ def path_BFS(
parent[n] = x
done = True
break
if n not in frontier and n not in explored:
if n not in seen:
# add it to the frontier
seen.add(n)
frontier.append(n)
if verbose:
print(" add", n.name, "to the frontier")
Expand All @@ -3122,8 +3128,9 @@ def path_BFS(
while x is not S:
p = parent[x]
length += self._require_cost(p.edgeto(x))
path.insert(0, p)
path.append(p)
x = p
path.reverse()

if summary or verbose:
print(
Expand Down Expand Up @@ -3184,8 +3191,14 @@ def path_UCS(
S = self._resolve_vertex(S, "start")
G = self._resolve_vertex(G, "goal")

frontier: list[Vertex] = [S]
explored: list[Vertex] = []
# The frontier is a dict, used as an ordered set: its order is the order
# vertices first joined it, which breaks ties between equal ``f``, and
# its value is that position. ``heap`` finds the minimum ``f``; a
# vertex that is reparented is pushed again, and the older entry is
# recognised as stale when it is popped.
frontier: dict[Vertex, int] = {S: 0}
heap: list[tuple[float, int, Vertex]] = [(0, 0, S)]
explored: dict[Vertex, None] = {}
parent: dict[Vertex, Vertex] = {}
f: dict[Vertex, float] = {S: 0} # evaluation function

Expand All @@ -3197,8 +3210,11 @@ def path_UCS(
)
print("EXPLORED:", ", ".join([str(v.name) for v in explored]))

i = np.argmin([f[n] for n in frontier]) # minimum f in frontier
x = frontier.pop(i)
while True: # minimum f in frontier, skipping stale heap entries
fx, _, x = heapq.heappop(heap)
if x in frontier and f[x] == fx:
break
del frontier[x]
if verbose:
print(" expand", x.name)
if x is G:
Expand All @@ -3212,7 +3228,8 @@ def path_UCS(
# add it to the frontier
parent[n] = x
f[n] = fnew
frontier.append(n)
frontier[n] = len(parent) # one entry per vertex added so far
heapq.heappush(heap, (fnew, frontier[n], n))
if verbose:
print(" add", n.name, "to the frontier")

Expand All @@ -3226,8 +3243,9 @@ def path_UCS(
)
f[n] = fnew
parent[n] = x
heapq.heappush(heap, (fnew, frontier[n], n))

explored.append(x)
explored[x] = None
if verbose:
print(" move", x.name, "to the explored list")
else:
Expand All @@ -3242,8 +3260,9 @@ def path_UCS(
while x is not S:
p = parent[x]
length += self._require_cost(p.edgeto(x))
path.insert(0, p)
path.append(p)
x = p
path.reverse()

parent_names: dict[str, str] = {}
for v, p in parent.items():
Expand Down Expand Up @@ -3310,8 +3329,10 @@ def path_Astar(
S = self._resolve_vertex(S, "start")
G = self._resolve_vertex(G, "goal")

frontier: list[Vertex] = [S]
explored: list[Vertex] = []
# see path_UCS for the frontier and heap
frontier: dict[Vertex, int] = {S: 0}
heap: list[tuple[float, int, Vertex]] = [(0, 0, S)]
explored: dict[Vertex, None] = {}
parent: dict[Vertex, Vertex] = {}
g: dict[Vertex, float] = {S: 0} # cost to come
f: dict[Vertex, float] = {S: 0} # evaluation function
Expand All @@ -3324,8 +3345,11 @@ def path_Astar(
)
print("EXPLORED:", ", ".join([str(v.name) for v in explored]))

i = np.argmin([f[n] for n in frontier]) # minimum f in frontier
x = frontier.pop(i)
while True: # minimum f in frontier, skipping stale heap entries
fx, _, x = heapq.heappop(heap)
if x in frontier and f[x] == fx:
break
del frontier[x]
if verbose:
print(" expand", x.name)
if x is G:
Expand All @@ -3336,10 +3360,11 @@ def path_Astar(
continue # self-loop, never part of a shortest path
if n not in frontier and n not in explored:
# add it to the frontier
frontier.append(n)
parent[n] = x
frontier[n] = len(parent) # one entry per vertex added so far
g[n] = g[x] + self._require_cost(e) # update cost to come
f[n] = g[n] + n.heuristic_distance(G) # heuristic
heapq.heappush(heap, (f[n], frontier[n], n))
if verbose:
print(" add", n.name, "to the frontier")
elif n in frontier:
Expand All @@ -3355,8 +3380,9 @@ def path_Astar(
f[n] = g[n] + n.heuristic_distance(G) # heuristic

parent[n] = x # reparent
heapq.heappush(heap, (f[n], frontier[n], n))

explored.append(x)
explored[x] = None
if verbose:
print(" move", x.name, "to the explored list")

Expand All @@ -3372,8 +3398,9 @@ def path_Astar(
while x is not S:
p = parent[x]
length += self._require_cost(p.edgeto(x))
path.insert(0, p)
path.append(p)
x = p
path.reverse()

parent_names: dict[str, str] = {}
for v, p in parent.items():
Expand Down
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