use stack
class Solution(object):
def calculate(self, s):
"""
:type s: str
:rtype: int
"""
stack=[]
num=0
sign='+'
for i in xrange(len(s)):
if s[i].isdigit():
num=num*10+int(s[i])
if (s[i]!=' ' and not s[i].isdigit()) or i==(len(s)-1):
if sign=='+':stack.append(num)
elif sign=='-':stack.append(-num)
elif sign=='*':
stack.append(stack.pop()*num)
elif sign=='/':
last_num=stack.pop()
if last_num/num<0 and last_num%num!=0:
temp=last_num/num+1
else:
temp=last_num/num
stack.append(temp)
sign=s[i]
num=0
return sum(stack)
use regular expression
class Solution(object):
def calculate(self, s):
"""
:type s: str
:rtype: int
"""
tokens=iter(re.findall(r'\d+|\S',s))
total=0
sign=1
for token in tokens:
if token in '+-':
total+=sign*cache
sign=' +'.find(token)
elif token in '*/':
n=int(next(tokens))
cache=cache*n if token=='*' else cache/n
else:
cache=int(token)
return total+sign*cache
