Implement a basic calculator to evaluate a simple expression string. The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empty spaces . Example 1: Input: "1 + 1" Output:
Implement a basic calculator to evaluate a simple expression string.
The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empty spaces .
Example 1:
Input: "1 + 1"
Output: 2
Example 2:
Input: " 2-1 + 2 "
Output: 3
Example 3:
Input: "(1+(4+5+2)-3)+(6+8)"
Output: 23
Note:
You may assume that the given expression is always valid. Do not use the eval built-in library function.
class Solution:
def calculate(self, s):
"""
:type s: str
:rtype: int
"""
num,sign,i = 0,1,0
op = []
while i <len(s):
if s[i].isdigit():
start = i
while i<len(s) and s[i].isdigit():
i += 1
n = int(s[start:i])
num += n * sign
continue
if s[i]==‘+‘:
sign = 1
i += 1
continue
if s[i]==‘-‘:
sign = -1
i += 1
continue
if s[i]==‘(‘:
op.append(num)
op.append(sign)
num = 0
sign = 1
i += 1
continue
if s[i]==‘)‘:
num = num * op.pop()
num += op.pop()
i += 1
continue
i += 1
return num