227. Basic Calculator II (M)

Implement a basic calculator to evaluate a simple expression string.

The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should truncate toward zero.

Example 1:

Input: "3+2*2"
Output: 7
Example 2:

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

Input: " 3+5 / 2 "
Output: 5
Note:

You may assume that the given expression is always valid.
Do not use the eval built-in library function.

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我的答案：参考了前面224题

class Solution {
public:
    int ret = 0;
    int val1 = 0;
    int val2 = 0;
    bool more = false;
    int sign = 1;
    bool plus;
    int calculate(string s) {
        for (int pos=0; pos