m0227.py

"""Basic Calculator II
Given a string s which represents an expression, evaluate this expression and
return its value.

The integer division should truncate toward zero.

Example 1:
Input: s = "3+2*2"
Output: 7

Example 2:
Input: s = " 3/2 "
Output: 1

Example 3:
Input: s = " 3+5 / 2 "
Output: 5

Constraints:
* 1 <= s.length <= 3 * 105
* s consists of integers and operators ('+', '-', '*', '/') separated by some
  number of spaces.
* s represents a valid expression.
* All the integers in the expression are non-negative integers in the range
  [0, 2^31 - 1].
* The answer is guaranteed to fit in a 32-bit integer.
"""