题解 | #表达式求值#

#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 返回表达式的值
# @param s string字符串 待计算的表达式
# @return int整型
#
class Solution:
    def solve(self , s: str) -> int:
        # write code here
        num = 0
        i = 0
        n = len(s)
        stack = []
        res = 0
        op = '+'
        while i < n:
            if s[i] >= '0' and s[i] <= '9':
                num = num * 10 + int(s[i])
            if s[i] == '(':
                cnt = 0
                j = i
                while i < n:
                    if s[i] == '(':
                        cnt += 1
                    elif s[i] == ')':
                        cnt -= 1
                    if cnt == 0:
                        break
                    i += 1
                num = self.solve(s[j + 1 : i])
            if s[i] == '+' or s[i] == '-' or s[i] == '*' or s[i] == '/' or i == n - 1:
                if op == '+':
                    stack.append(num)
                elif op == '-':
                    stack.append(-num)
                elif op == '*':
                    stack[-1] *= num;
                else:
                    if stack[-1] > 0:
                        stack[-1] /= num
                    else:
                        t = -stack[-1] / num
                        stack[-1] = -t
                num = 0
                op = s[i]
            i += 1
        while stack:
            res += stack.pop()
        return res