mirror of
https://github.com/kuhyx/praca_magisterska.git
synced 2026-07-04 14:43:07 +02:00
233 lines
7.9 KiB
Python
233 lines
7.9 KiB
Python
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"""
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Shortest-path algorithms: Dijkstra, Bellman-Ford, A*
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Pure implementations — no GUI dependencies.
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"""
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import heapq
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import math
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from dataclasses import dataclass, field
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from typing import Optional
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INF = float("inf")
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# ─── Graph ───────────────────────────────────────────────────────────────
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NODES: dict[str, tuple[int, int]] = {
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"S": (80, 350), "A": (270, 130), "B": (270, 570),
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"C": (500, 80), "D": (500, 350), "E": (500, 620),
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"F": (730, 180), "G": (730, 520), "T": (950, 350),
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}
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EDGES: list[tuple[str, str, int]] = [
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("S", "A", 4), ("S", "B", 2), ("A", "C", 5), ("A", "D", 10),
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("B", "D", 3), ("B", "E", 8), ("C", "F", 3), ("D", "F", 7),
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("D", "G", 4), ("E", "G", 2), ("F", "T", 4), ("G", "T", 6),
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("C", "D", 2),
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]
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ADJ: dict[str, list[tuple[str, int]]] = {n: [] for n in NODES}
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for _u, _v, _w in EDGES:
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ADJ[_u].append((_v, _w))
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ADJ[_v].append((_u, _w))
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SOURCE = "S"
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GOAL = "T"
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def heuristic(node: str) -> float:
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x1, y1 = NODES[node]
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x2, y2 = NODES[GOAL]
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return math.hypot(x2 - x1, y2 - y1) / 100
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# ─── State ───────────────────────────────────────────────────────────────
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@dataclass
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class AlgoState:
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dist: dict[str, float] = field(default_factory=dict)
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prev: dict[str, Optional[str]] = field(default_factory=dict)
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visited: set[str] = field(default_factory=set)
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finished: bool = False
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step: int = 0
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message: str = ""
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path: list[str] = field(default_factory=list)
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relaxed_edges: set[tuple[str, str]] = field(default_factory=set)
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current_node: Optional[str] = None
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f_score: dict[str, float] = field(default_factory=dict)
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frontier: list = field(default_factory=list) # heap for Dijkstra/A*
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bf_iteration: int = 0
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def _reconstruct_path(self) -> None:
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path: list[str] = []
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node: Optional[str] = GOAL
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while node is not None:
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path.append(node)
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node = self.prev.get(node)
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path.reverse()
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self.path = path if path and path[0] == SOURCE else []
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# ─── Dijkstra ────────────────────────────────────────────────────────────
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def dijkstra_init() -> AlgoState:
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st = AlgoState()
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st.dist = {n: INF for n in NODES}
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st.prev = {n: None for n in NODES}
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st.dist[SOURCE] = 0
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st.frontier = [(0, SOURCE)]
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st.message = f"Dijkstra: start from {SOURCE}, dist[{SOURCE}]=0"
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return st
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def dijkstra_step(st: AlgoState) -> None:
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if st.finished or not st.frontier:
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st.finished = True
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st._reconstruct_path()
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c = st.dist.get(GOAL, INF)
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st.message = (f"Dijkstra done! Path: {'→'.join(st.path)}, cost={c:.0f}"
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if st.path else "Dijkstra done! No path.")
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return
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st.current_node = None
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while st.frontier:
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d, u = heapq.heappop(st.frontier)
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if u in st.visited:
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continue
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st.visited.add(u)
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st.step += 1
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st.current_node = u
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st.message = f"Step {st.step}: visit {u} (dist={st.dist[u]:.0f})"
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for v, w in ADJ[u]:
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if v not in st.visited:
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nd = st.dist[u] + w
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if nd < st.dist[v]:
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st.dist[v] = nd
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st.prev[v] = u
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heapq.heappush(st.frontier, (nd, v))
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st.relaxed_edges.add((u, v))
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st.message += f" | relax {u}->{v}:{nd:.0f}"
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return
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st.finished = True
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st._reconstruct_path()
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c = st.dist.get(GOAL, INF)
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st.message = (f"Dijkstra done! Path: {'→'.join(st.path)}, cost={c:.0f}"
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if st.path else "Dijkstra done! No path.")
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# ─── Bellman-Ford ────────────────────────────────────────────────────────
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def bellman_ford_init() -> AlgoState:
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st = AlgoState()
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st.dist = {n: INF for n in NODES}
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st.prev = {n: None for n in NODES}
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st.dist[SOURCE] = 0
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st.message = (f"Bellman-Ford: {len(NODES)-1} iterations "
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f"over {len(EDGES)*2} directed edges")
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return st
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def bellman_ford_step(st: AlgoState) -> None:
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if st.finished:
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return
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V = len(NODES)
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all_edges = ([(u, v, w) for u, v, w in EDGES]
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+ [(v, u, w) for u, v, w in EDGES])
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if st.bf_iteration < V - 1:
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changed = False
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for src, dst, w in all_edges:
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if st.dist[src] + w < st.dist[dst]:
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st.dist[dst] = st.dist[src] + w
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st.prev[dst] = src
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st.relaxed_edges.add((src, dst))
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st.visited.add(src)
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st.visited.add(dst)
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changed = True
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st.bf_iteration += 1
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st.step += 1
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st.current_node = None
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label = "changes made" if changed else "no changes (stable)"
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st.message = f"Iteration {st.bf_iteration}/{V-1}: {label}"
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if not changed:
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st.finished = True
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st._reconstruct_path()
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c = st.dist.get(GOAL, INF)
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st.message += (f" -> Early stop! Path: {'→'.join(st.path)}, cost={c:.0f}"
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if st.path else " -> Early stop!")
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else:
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neg = any(st.dist[s] + w < st.dist[d] for s, d, w in all_edges)
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st.finished = True
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if neg:
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st.message = "Negative cycle detected!"
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else:
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st._reconstruct_path()
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c = st.dist.get(GOAL, INF)
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st.message = (f"Bellman-Ford done! Path: {'→'.join(st.path)}, cost={c:.0f}"
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if st.path else "Bellman-Ford done! No path.")
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# ─── A* ──────────────────────────────────────────────────────────────────
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def astar_init() -> AlgoState:
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st = AlgoState()
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st.dist = {n: INF for n in NODES}
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st.prev = {n: None for n in NODES}
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st.f_score = {n: INF for n in NODES}
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st.dist[SOURCE] = 0
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h = heuristic(SOURCE)
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st.f_score[SOURCE] = h
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st.frontier = [(h, SOURCE)]
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st.message = f"A*: start={SOURCE}, goal={GOAL}, h({SOURCE})={h:.1f}"
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return st
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def astar_step(st: AlgoState) -> None:
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if st.finished or not st.frontier:
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st.finished = True
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st._reconstruct_path()
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c = st.dist.get(GOAL, INF)
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st.message = (f"A* done! Path: {'→'.join(st.path)}, cost={c:.0f}"
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if st.path else "A* done! No path.")
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return
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st.current_node = None
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while st.frontier:
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f, u = heapq.heappop(st.frontier)
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if u in st.visited:
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continue
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st.visited.add(u)
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st.step += 1
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st.current_node = u
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if u == GOAL:
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st.finished = True
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st._reconstruct_path()
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st.message = (f"Step {st.step}: GOAL reached! "
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f"Path: {'→'.join(st.path)}, cost={st.dist[GOAL]:.0f}")
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return
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h = heuristic(u)
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st.message = (f"Step {st.step}: visit {u} "
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f"(g={st.dist[u]:.0f}, h={h:.1f}, f={f:.1f})")
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for v, w in ADJ[u]:
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if v not in st.visited:
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nd = st.dist[u] + w
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if nd < st.dist[v]:
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st.dist[v] = nd
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st.prev[v] = u
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fv = nd + heuristic(v)
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st.f_score[v] = fv
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heapq.heappush(st.frontier, (fv, v))
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st.relaxed_edges.add((u, v))
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st.message += f" | relax {u}->{v}: g={nd:.0f}, f={fv:.1f}"
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return
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st.finished = True
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st._reconstruct_path()
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st.message = "A* done! No path."
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