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def aStarAlgo(start_node, stop_node): open_set = set(start_node) closed_set = set() g = {} #store distance from starting node parents = {}# parents contains an adjacency map of all nodes #ditance of starting node from itself is zero g[start_node] = 0 #start_node is root node i.e it has no parent nodes #so start_node is set to its own parent node parents[start_node] = start_node while len(open_set) > 0: n = None #node with lowest f() is found for v in open_set: if n == None or g[v] + heuristic(v) < g[n] + heuristic(n): n = v if n == stop_node or Graph_nodes[n] == None: pass else: for (m, weight) in get_neighbors(n): #nodes 'm' not in first and last set are added to first #n is set its parent if m not in open_set and m not in closed_set: open_set.add(m) parents[m] = n g[m] = g[n] + weight #for each node m,compare its distance from start i.e g(m) to the #from start through n node else: if g[m] > g[n] + weight: #update g(m) g[m] = g[n] + weight #change parent of m to n parents[m] = n #if m in closed set,remove and add to open if m in closed_set: closed_set.remove(m) open_set.add(m) if n == None: print('Path does not exist!') return None # if the current node is the stop_node # then we begin reconstructin the path from it to the start_node if n == stop_node: path = [] while parents[n] != n: path.append(n) n = parents[n] path.append(start_node) path.reverse() print('Path found: {}'.format(path)) return path # remove n from the open_list, and add it to closed_list # because all of his neighbors were inspected open_set.remove(n) closed_set.add(n) print('Path does not exist!') return None #define fuction to return neighbor and its distance #from the passed node def get_neighbors(v): if v in Graph_nodes: return Graph_nodes[v] else: return None #for simplicity we ll consider heuristic distances given #and this function returns heuristic distance for all nodes def heuristic(n): H_dist = { 'A': 11, 'B': 6, 'C': 99, 'D': 1, 'E': 7, 'G': 0, 'H': 32, 'I': 12, 'J': 23 } return H_dist[n] #Describe your graph here Graph_nodes = { 'A': [('B', 2), ('E', 3)], 'B': [('D', 1), ('G', 9)], 'C': None, 'E': [('D', 6)], 'F': [('A', 1)], 'G': [('B', 10), ('H', 10)], 'D': [('G', 1)], 'H': [('I', 12)], 'I': [('J', 11), ('B', 2)], 'J': [('C', 10)] } aStarAlgo('A', 'J')