[Leetcode] Basic Calculator II, Solution

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.

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 eval built-in library function.

[Thoughts]
没有括号，简单了很多。实现看code

[Code]

1:    int calculate(string s) {  
2:      istringstream in(s+ "+");  
3:        
4:      int num, total = 0, n;  
5:      char op;  
6:      in>>num;  
7:      while(in>>op) {  
8:        if(op == '+' || op == '-'){  
9:          total += num;  
10:          in>>num;  
11:          num = op=='-'? -num:num;  
12:        } else {  
13:          in>>n;  
14:          if(op == '*') {  
15:            num *=n;  
16:          } else {  
17:            num /=n;  
18:          }  
19:        }  
20:      }  
21:      return total;  
22:    }