def is_balanced(input_str):
mys = ArrayStack()
lst = input_str.split()
fore = "([{"
back = ")]}"
for i in range(len(lst)):
if lst[i] in fore:
myStack.push(lst[i])
else:
if lst[i] not in back:
raise Exception("invalid input!")
else:
lst[i] = mine
if mys.is_empty() == False:
curr = myStack.pop()
else:
return False
if curr == '(' and mine != ')': #mind == syntax!!!
return False
elif curr == '[' and mine != ']':
return False
elif curr == '{' and mine != '}':
return False
if mys.is_empty() == False:
return False
return True
class MaxStack:
def __init__(self):
self._data = ArrayStack()
def is_empty(self):
return len(self._data) == 0
def __len__(self):
return len(self._data)
def push(self, e):
if len(self._data) == 0:
elem = (e, e)
self._data.push(elem)
else:
last = self._data.top()
mymax = last[1]
currmax = mymax
if e > mymax:
currmax = e
tup1 = (e, currmax)
self._data.push(tup1)
def top(self):
if self.is_empty():
raise Empty("MaxStack is empty")
##return a reference without removing it
temp = self._data.top()
return temp[0]
def pop(self):
if self.is_empty():
raise Empty("MaxStack is empty")
temp = self._data.top()
self._data.pop() ##Can I directly operate on the LL array??
return temp[0]
def max(self):
## theta 1 worst-case time
if self.is_empty():
raise Empty("MaxStack is empty")
temp = self._data.top()
return temp[1]
def eval_postfix(exp_str):
str_lst = exp_str.split(" ")
operators = "+-*/"
mystack = ArrayStack()
for item in str_lst:
if item not in operators:
mystack.push(int(item)) #KEY is to convert to int!!!
else:
arg2 = mystack.pop()
arg1 = mystack.pop() #ARG2 popped first!!!
if item == '+':
res = arg1 + arg2
elif item == '-':
res = arg1 - arg2
elif item == '*':
res = arg1 * arg2
else:
res = arg1 / arg2
mystack.push(res)
return mystack.pop()
def permutations(lst):
## non-recursive
## alloed a Stack, a Queue, Theta 1 additional space
# use stack to generate permutations, use queue to store partial collection of pers generated so far
# queue set up to hold
mystack = ArrayStack()
length = math.factorial(len(lst))
result = ArrayQueue(length)
for i in range(len(lst)):
mystack.push(lst[i])
lst1 = [mystack.pop()]
result.enqueue(lst1)
while mystack.is_empty() == False:
elem = mystack.pop()
times = math.factorial(len(result.first()))
for i in range(times):
lst1 = result.dequeue()
for i in range(len(lst1) + 1):
newlst = copy.deepcopy(lst1)
newlst.insert(i, elem)
result.enqueue(newlst)
return result
def eval_prefix(exp_str):
str_lst = exp_str.split(" ")
operators = "+-*/"
mystack = ArrayStack()
count1 = 0
count2 = 0
count3 = 0
for i in range(len(str_lst)): # for i in range
if count2 != 0 and count1 != 0:
arg2 = mystack.pop()
arg1 = mystack.pop()
item = mystack.pop()
if item == '+':
res = arg1 + arg2
elif item == '-':
res = arg1 - arg2
elif item == '*':
res = arg1 * arg2
else:
res = arg1 / arg2
mystack.push(res)
count1 = 0
count3 = 1
if (count1 != 0) and (str_lst[i] not in operators) and (count2 == 0):
continue
if (count3 != 0):
count3 = 0
continue
if str_lst[i] in operators:
mystack.push(str_lst[i])
count1 = 0
else:
arg1 = int(str_lst[i]) ##CONVERT to int!!
if count2 == 0 and count1 == 0:
arg2 = int(str_lst[i+1])
count1 += 1
item = mystack.pop()
if item == '+':
res = arg1 + arg2
elif item == '-':
res = arg1 - arg2
elif item == '*':
res = arg1 * arg2
else:
res = arg1 / arg2
mystack.push(res)
if (i+2 <= len(str_lst)-1):
if str_lst[i+2] not in operators:
count2 += 1
else:
arg2 = arg1
arg1 = int(mystack.pop())
item = mystack.pop()
if item == '+':
res = arg1 + arg2
elif item == '-':
res = arg1 - arg2
elif item == '*':
res = arg1 * arg2
else:
res = arg1 / arg2
mystack.push(res)
return res
def __init__(self):
self._data = ArrayStack()