def evaluate_infix(infix_expression):
"""
Evaluates an infix expression.
Numerical operands must be integers.
>>> evaluate_infix('2 + 3 * 4')
14
>>> evaluate_infix('2 + (3 * 4)')
14
>>> evaluate_infix('(2 + 3) * 4')
20
>>> evaluate_infix('2 + 3 * 2 - 5')
3
>>> evaluate_infix('(2 + 3) * (2 - 5)')
-15
>>> evaluate_infix('(2 + 3) * (5 / 2)')
12.5
"""
# Split infix string into tokens. For example:
# '2+3*4' => ['2', '+', '3', '*', '4']
tokens = re.findall(r'(\d+|\*|\+|\/|\-|\)|\(|\^)', infix_expression)
operator = Stack()
operand = Stack()
for s in tokens:
if s not in OP_PREC: #s is an integer
operand.push(s)
elif s == '(':
operator.push(s)
elif s == ')':
item = operator.pop()
while item != '(':
alpha = float(operand.pop())
beta = float(operand.pop())
if item == '(':
operator.pop()
else:
delta = calculate(item, beta, alpha)
operand.push(delta)
item = operator.pop()
else: #s is an operator
if len(operator) > 1 and len(operand) > 2:
if OP_PREC[s] < OP_PREC[operator.peek()]:
sign = operator.pop()
alpha = float(operand.pop())
beta = float(operand.pop())
delta = calculate(sign, beta, alpha)
operand.push(delta)
operator.push(s)
while not operand.is_empty() and not operator.is_empty():
sign = operator.pop()
alpha = float(operand.pop())
beta = float(operand.pop())
delta = calculate(sign, beta, alpha)
operand.push(delta)
result = operand.pop()
if result % int(result) == 0:
result = round(result)
return result
def infix_to_postfix(infix_expression):
"""
Converts an infix expression to a postfix expression.
Numerical operands must be integers.
>>> infix_to_postfix('2 + 3')
'2 3 +'
>>> infix_to_postfix('2 + 3 * 4')
'2 3 4 * +'
>>> infix_to_postfix('(2 + 3) * 4')
'2 3 + 4 *'
>>> infix_to_postfix('2 + 3 * 2 - 5')
'2 3 2 * + 5 -'
>>> infix_to_postfix('(2 + 3) * (2 - 5)')
'2 3 + 2 5 - *'
>>> infix_to_postfix('(2 + 3) * (5 / 2)')
'2 3 + 5 2 / *'
"""
# Split infix string into tokens. For example:
# '2+3*4' => ['2', '+', '3', '*', '4']
tokens = re.findall(r'(\d+|\*|\+|\/|\-|\)|\(|\^)', infix_expression)
output = []
stack = Stack()
for s in tokens:
if s not in OP_PREC:
output.append(s)
elif s == '(':
stack.push(s)
elif s == ')':
item = stack.pop()
while item != '(':
output.append(item)
item = stack.pop()
else:
while not stack.is_empty() and OP_PREC[s] <= OP_PREC[stack.peek()]:
output.append(stack.peek())
stack.pop()
stack.push(s)
while not stack.is_empty():
output.append(stack.pop())
string = ''
count = 0
for i in range(len(output) - 1):
string += output[i]
string += ' '
count += 1
string += output[-1]
return string
def depth_first_search(self, board):
moves = ['Up', 'Down', 'Left', 'Right'][::-1]
frontier = Stack()
explored = set()
frontier.push(State(board))
nodes_expanded = 0
while not frontier.is_empty():
curr = frontier.pop()
explored.add(curr)
if curr.board == self.goalBoard:
return curr, nodes_expanded
nodes_expanded += 1
for move in moves:
result = curr.board.move(move)
if result is not None:
result_state = State(result, move, curr, curr.depth + 1)
if result_state not in explored and result_state not in frontier:
State.max_depth = max(State.max_depth, result_state.depth)
frontier.push(result_state)
