题解 | #表达式求值#
表达式求值
https://www.nowcoder.com/practice/c215ba61c8b1443b996351df929dc4d4
一眼看过去很简单，实际写的时候发现很多坑。
1.第一步：先不管括号的问题
2.第二步：先不管乘法问题
3.第三步：实现加减运算
4.第四步：解决连续数字问题
class Solution:
def solve(self, s: str) -> int:
num, opt, stack = 0, '+', []
while s:
item,s = s[0],s[1:]
if(item=='('):
lens,end = 1,0
while lens > 0:
if s[end] == '(':
lens += 1
if s[end] == ')':
lens -= 1
end += 1
num = self.solve(s[0:end - 1])
s = s[end:]
elif item.isdigit():
num = num*10+int(item)
if not item.isdigit() or not s:
if opt == '+':
stack.append(num)
elif opt == '-':
stack.append(-num)
elif opt =='*':
stack.append(stack.pop()*num)
num,opt =0, item
return sum(stack)
