ANSWER:-


# Solves a randomized 8-puzzle using A* algorithm with plug-in heuristics

import random
import math

_goal_state = [[1,2,3],
[4,5,6],
[7,8,0]]

def index(item, seq):
"""Helper function that returns -1 for non-found index value of a seq"""
if item in seq:
return seq.index(item)
else:
return -1

class EightPuzzle:

def __init__(self):
# heuristic value
self._hval = 0
# search depth of current instance
self._depth = 0
# parent node in search path
self._parent = None
self.adj_matrix = []
for i in range(3):
self.adj_matrix.append(_goal_state[i][:])

def __eq__(self, other):
if self.__class__ != other.__class__:
return False
else:
return self.adj_matrix == other.adj_matrix

def __str__(self):
res = ''
for row in range(3):
res += ' '.join(map(str, self.adj_matrix[row]))
res += '\r\n'
return res

def _clone(self):
p = EightPuzzle()
for i in range(3):
p.adj_matrix[i] = self.adj_matrix[i][:]
return p

def _get_legal_moves(self):
"""Returns list of tuples with which the free space may
be swapped"""
# get row and column of the empty piece
row, col = self.find(0)
free = []
  
# find which pieces can move there
if row > 0:
free.append((row - 1, col))
if col > 0:
free.append((row, col - 1))
if row < 2:
free.append((row + 1, col))
if col < 2:
free.append((row, col + 1))

return free

def _generate_moves(self):
free = self._get_legal_moves()
zero = self.find(0)

def swap_and_clone(a, b):
p = self._clone()
p.swap(a,b)
p._depth = self._depth + 1
p._parent = self
return p

return map(lambda pair: swap_and_clone(zero, pair), free)

def _generate_solution_path(self, path):
if self._parent == None:
return path
else:
path.append(self)
return self._parent._generate_solution_path(path)

def solve(self, h):
"""Performs A* search for goal state.
h(puzzle) - heuristic function, returns an integer
"""
def is_solved(puzzle):
return puzzle.adj_matrix == _goal_state

openl = [self]
closedl = []
move_count = 0
while len(openl) > 0:
x = openl.pop(0)
move_count += 1
if (is_solved(x)):
if len(closedl) > 0:
return x._generate_solution_path([]), move_count
else:
return [x]

succ = x._generate_moves()
idx_open = idx_closed = -1
for move in succ:
# have we already seen this node?
idx_open = index(move, openl)
idx_closed = index(move, closedl)
hval = h(move)
fval = hval + move._depth

if idx_closed == -1 and idx_open == -1:
move._hval = hval
openl.append(move)
elif idx_open > -1:
copy = openl[idx_open]
if fval < copy._hval + copy._depth:
# copy move's values over existing
copy._hval = hval
copy._parent = move._parent
copy._depth = move._depth
elif idx_closed > -1:
copy = closedl[idx_closed]
if fval < copy._hval + copy._depth:
move._hval = hval
closedl.remove(copy)
openl.append(move)

closedl.append(x)
openl = sorted(openl, key=lambda p: p._hval + p._depth)

# if finished state not found, return failure
return [], 0

def shuffle(self, step_count):
for i in range(step_count):
row, col = self.find(0)
free = self._get_legal_moves()
target = random.choice(free)
self.swap((row, col), target)
row, col = target

def find(self, value):
"""returns the row, col coordinates of the specified value
in the graph"""
if value < 0 or value > 8:
raise Exception("value out of range")

for row in range(3):
for col in range(3):
if self.adj_matrix[row][col] == value:
return row, col
  
def peek(self, row, col):
"""returns the value at the specified row and column"""
return self.adj_matrix[row][col]

def poke(self, row, col, value):
"""sets the value at the specified row and column"""
self.adj_matrix[row][col] = value

def swap(self, pos_a, pos_b):
"""swaps values at the specified coordinates"""
temp = self.peek(*pos_a)
self.poke(pos_a[0], pos_a[1], self.peek(*pos_b))
self.poke(pos_b[0], pos_b[1], temp)


def heur(puzzle, item_total_calc, total_calc):
"""
Heuristic template that provides the current and target position for each number and the
total function.
  
Parameters:
puzzle - the puzzle
item_total_calc - takes 4 parameters: current row, target row, current col, target col.
Returns int.
total_calc - takes 1 parameter, the sum of item_total_calc over all entries, and returns int.
This is the value of the heuristic function
"""
t = 0
for row in range(3):
for col in range(3):
val = puzzle.peek(row, col) - 1
target_col = val % 3
target_row = val / 3

# account for 0 as blank
if target_row < 0:
target_row = 2

t += item_total_calc(row, target_row, col, target_col)

return total_calc(t)

//The initial state, you can def the set function and set it in the main function.

p.set("123456078")

def set(self, other) :
i=0;
for row in range(3):
for col in range(3):
self.adj_matrix[row][col] = int(other[i])
i=i+1
Public Answer
