implemented a_star with simple heuristics

main.py

@@ -7,7 +7,7 @@ from pyglet.gl import *  # for blocky textures
 # other files of this project
 import project_constants as const
 import minefield as mf
-import searching_algorithms.bfs as bfs
+import searching_algorithms.a_star as a_star
 from display_assets import blit_graphics
 
 
@@ -27,8 +27,8 @@ def main():
     minefield = mf.Minefield(const.MAP_RANDOM_10x10)
 
     # get sequence of actions found by BFS algorithm
-    action_sequence = bfs.graphsearch(
-        initial_state=bfs.State(
+    action_sequence = a_star.graphsearch(
+        initial_state=a_star.State(
             row=minefield.agent.position[0],
             column=minefield.agent.position[1],
             direction=const.Direction.UP),

searching_algorithms/a_star.py

@@ -0,0 +1,184 @@
+from __future__ import annotations
+
+from heapq import heappush, heappop, heapify
+from typing import List
+import itertools
+import ctypes
+
+from project_constants import Direction, Action
+from minefield import Minefield
+
+# temporary goal for testing
+GOAL = (2, 6)
+
+
+class State:
+    def __init__(self, row, column, direction: Direction):
+        self.row = row
+        self.column = column
+        self.direction = direction
+
+
+class Node:
+    def __init__(self, state: State, parent: Node = None, action: Action = None, weight=0):
+        self.state = state
+        self.parent = parent
+        self.action = action
+
+        if not weight:
+            self.weight = self._get_weight()
+        else:
+            self.weight = weight
+
+    def _get_weight(self):
+        weight = 0
+        if self.parent is not None:
+            weight += self.parent.weight
+
+        heuristics = abs(self.state.row - GOAL[0]) + abs(self.state.column - GOAL[1])
+        weight += heuristics
+
+        return weight
+
+
+def goal_test(state: State):
+    if (state.row, state.column) == GOAL:
+        return True
+    return False
+
+
+def get_successors(state: State, minefield: Minefield):
+    successors = list()
+
+    state_left = State(state.row, state.column, state.direction.previous())
+    successors.append((Action.ROTATE_LEFT, state_left))
+
+    state_right = State(state.row, state.column, state.direction.next())
+    successors.append((Action.ROTATE_RIGHT, state_right))
+
+    target = go(state.row, state.column, state.direction)
+
+    if minefield.is_valid_move(target[0], target[1]):
+        state_go = State(target[0], target[1], state.direction)
+        successors.append((Action.GO, state_go))
+
+    return successors
+
+
+def graphsearch(initial_state: State, minefield: Minefield, fringe: List[Node] = None, explored: List[Node] = None):
+    # reset global priority queue helpers
+    global entry_finder
+    global counter
+    entry_finder = {}
+    counter = itertools.count()
+
+    # fringe and explored initialization
+    if fringe is None:
+        fringe = list()
+        heapify(fringe)
+    if explored is None:
+        explored = list()
+
+    explored_states = set()
+    fringe_states = set()
+
+    # root Node
+    add_node(fringe, Node(initial_state))
+    fringe_states.add((initial_state.row, initial_state.column, initial_state.direction))
+
+    while True:
+        # fringe empty -> solution not found
+        if not any(fringe):
+            ctypes.windll.user32.MessageBoxW(0, "Brak rozwiązania", "GAME OVER", 1)
+            return []
+
+        # get first element from fringe
+        element = pop_node(fringe)
+        if element is None:
+            ctypes.windll.user32.MessageBoxW(0, "Brak rozwiązania", "GAME OVER", 1)
+            return []
+
+        fringe_states.remove((element.state.row, element.state.column, element.state.direction))
+
+        # if solution was found, prepare and return actions sequence
+        if goal_test(element.state):
+            actions_sequence = [element.action]
+            parent = element.parent
+
+            while parent is not None:
+                # root's action will be None, don't add it
+                if parent.action is not None:
+                    actions_sequence.append(parent.action)
+                parent = parent.parent
+
+            actions_sequence.reverse()
+            return actions_sequence
+
+        # add current node to explored (prevents infinite cycles)
+        explored.append(element)
+        explored_states.add((element.state.row, element.state.column, element.state.direction))
+
+        # loop through every possible next action
+        for successor in get_successors(element.state, minefield):
+
+            new_node = Node(state=successor[1],
+                            parent=element,
+                            action=successor[0])
+            successor_state = (successor[1].row, successor[1].column, successor[1].direction)
+
+            if successor_state not in fringe_states and \
+                    successor_state not in explored_states:
+
+                add_node(fringe, new_node)
+                fringe_states.add((new_node.state.row, new_node.state.column, new_node.state.direction))
+
+            # update weight if it's lower
+            elif successor_state in fringe and entry_finder[successor_state][0] > new_node.weight:
+                update_priority(fringe, new_node)
+
+            else:
+                del new_node
+
+
+# TEMPORARY METHOD
+def go(row, column, direction):
+    target = tuple()
+
+    if direction == Direction.RIGHT:
+        target = row, column + 1
+    elif direction == Direction.LEFT:
+        target = row, column - 1
+    elif direction == Direction.UP:
+        target = row - 1, column
+    elif direction == Direction.DOWN:
+        target = row + 1, column
+
+    return target
+
+
+# PRIORITY QUEUE HANDLER
+entry_finder = {}               # mapping of states to entries in a heap
+REMOVED = '<removed-node>'      # placeholder for a removed nodes
+counter = itertools.count()     # unique sequence count
+
+
+def add_node(heap, node: Node):
+    count = next(counter)
+    entry = [node.weight, count, node]
+    entry_finder[node.state] = entry
+    heappush(heap, entry)
+
+
+def pop_node(heap):
+    while heap:
+        priority, count, node = heappop(heap)
+        if node is not REMOVED:
+            del entry_finder[node.state]
+            return node
+    return None
+
+
+def update_priority(heap, new_node):
+    old_entry = entry_finder.pop(new_node.state)
+    old_entry[-1] = REMOVED
+    add_node(heap, new_node)