[leetcode]224. Basic Calculator

Implement a basic calculator to evaluate a simple expression string.

The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empty spaces .

You may assume that the given expression is always valid.

Some examples:
"1 + 1" = 2
" 2-1 + 2 " = 3
"(1+(4+5+2)-3)+(6+8)" = 23
Note: Do not use the eval built-in library function.

题目说模仿一个计算器，做加减法，不过要注意括弧跟空格，空格就直接跳吧然后其他的保存下来，用栈分别存储数字括弧跟运算符，每遇到一个”）“就弹栈运算，数字跟括弧放一起，不过其实这样不太好，因为得为括弧设定一个特定的数，因为这个WA了一次。

class Solution {
public:
    stack<int> s_num;
    stack<char> fuhao;
    int count_f=0;
    void cal_sub(){
        if(s_num.size()<2)
            return;
        stack<int> nums;
        stack<char> cal;
        int b=s_num.top();
        s_num.pop();
        nums.push(b);
        int a=s_num.top();
        s_num.pop();
        char c;
        while(a!=-11111111){
            c=fuhao.top();
            fuhao.pop();

            nums.push(a);
            cal.push(c);
            if(s_num.size()>0){
                a=s_num.top();
                s_num.pop();
            }
            else
                a=-11111111;
        }
        count_f--;
        a=nums.top();
        nums.pop();
        while(nums.size()>0){
            b=nums.top();
            nums.pop();
            c=cal.top();
            cal.pop();
            if(c=='+')
                a=a+b;
            if(c=='-')
                a=a-b;
        }
        s_num.push(a);


    }
    int string2num(string s){
        string c_num;
        for(int i=0;i<s.size();i++){
            if(s[i]=='('){
                s_num.push(-11111111);
                count_f++;
            }
            if(s[i]>='0' && s[i]<='9')
                c_num+=s[i];
            if(s[i]==')') {
                if(c_num!="")
                    s_num.push(atoi(c_num.c_str()));
                c_num="";
                cal_sub();
            }
            if(s[i]=='+' || s[i]=='-') {
                if(c_num!="")
                    s_num.push(atoi(c_num.c_str()));
                c_num="";
                fuhao.push(s[i]);
            }
        }
        if(c_num!="")
            s_num.push(atoi(c_num.c_str()));
        cal_sub();
        return s_num.top();
    }
    int calculate(string s) {
        return string2num(s);
    }
};