Basic Calculator II

Implement a basic calculator to eva luate a simple expression string.

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

You may assume that the given expression is always valid.

Some examples:

"3+2*2" = 7
" 3/2 " = 1
" 3+5 / 2 " = 5

Note: Do not use the eva l built-in library function.

Credits:
Special thanks to @ts for adding this problem and creating all test cases.

解题思路：

同Basic Calculator I一样，只需改动转化成后缀表达式的代码。

class Solution {
public:
    int calculate(string s) {
        string postS = getPostString(s);    //获得后缀表达式
        cout << postS;
        stack
  
    nums;
        int len = postS.length();
        int num1, num2;
        for (int i = 0; i
   
    = '0' && postS[i] <= '9'){ num = num * 10 + (postS[i] - '0'); i++; } i--; nums.push(num); break; } } return nums.top(); } private: string getPostString(string s){ string postS = ""; stack
    
      op; int len = s.length(); for (int i = 0; i
     
      = '0'&&s[i] <= '9'){ postS += s[i]; i++; } postS += '#'; //分隔数字 i--; break; } } while (!op.empty()){ postS += op.top(); op.pop(); } return postS; } };