def __init__(self, regex):
"""
Initializes the NFA from the specified regular expression.
:param regex: the regular expression
"""
self.regex = regex
m = len(regex)
self.m = m
ops = Stack()
graph = Digraph(m + 1)
for i in range(0, m):
lp = i
if (regex[i] == '(' or regex[i] == '|'):
ops.push(i)
elif (regex[i] == ')'):
or_ = ops.pop()
# 2-way or operator
if (regex[or_] == '|'):
lp = ops.pop()
graph.add_edge(lp, or_ + 1)
graph.add_edge(or_, i)
elif (regex[or_] == '('):
lp = or_
else:
assert False
if (i < m - 1 and regex[i + 1] == '*'):
graph.add_edge(lp, i + 1)
graph.add_edge(i + 1, lp)
if (regex[i] == '(' or regex[i] == '*' or regex[i] == ')'):
graph.add_edge(i, i + 1)
if (ops.size() != 0):
raise ValueError("Invalid regular expression")
self.graph = graph
def evaluate():
ops = Stack()
vals = Stack()
while not stdio.isEmpty():
# Read token, push if operator
s = stdio.readString()
if s == "(": pass
elif s == "+": ops.push(s)
elif s == "-": ops.push(s)
elif s == "*": ops.push(s)
elif s == "/": ops.push(s)
elif s == "sqrt": ops.push(s)
elif s == ")":
# Pop, evaluate and push result if token is ")"
op = ops.pop()
v = vals.pop()
if op == "+": v = vals.pop() + v
elif op == "-": v = vals.pop() - v
elif op == "*": v = vals.pop() * v
elif op == "/": v = vals.pop() / v
elif op == "sqrt": v = math.sqrt(v)
vals.push(v)
else:
vals.push(float(s))
stdio.writeln(vals.pop())
