leetcode227

逆波蘭

主要思想，先搞乘除，最後一

class Solution {
public:
    
    int getNum(int num1,int num2,char op)
    {
        if(op == '+') return num1+num2;
        if(op == '-') return num1-num2;
        if(op == '*') return num1*num2;
        else return num1/num2;
    }
    int calculate(string s) {
        stack<long>num,num1;
        stack<char>op,op1;// +  -
        
        for(int i = 0;i<s.size();i++)
        {
            if(isdigit(s[i]))
            {
                long t = s[i]-'0';
                while(isdigit(s[i+1]))
                {
                    i++;
                    t = 10*t + s[i]-'0';
                    
                }
                num.push(t);
            }
            else if(s[i] == '*' || s[i] == '/')
            {
                long num1 = num.top();
                char op1 = s[i];
                num.pop();
                i++;

                long num2 = 0;
                while(!isdigit(s[i]))
                {
                    i++;
                }
                while(isdigit(s[i]))
                {
                    num2 = num2*10 + s[i] - '0';
                    i++;
                }
                i--;
                
                num.push(getNum(num1,num2,op1));
            }
            else if(s[i] == '+' || s[i] == '-') op.push(s[i]);
        }
        
        while(!op.empty())
        {
            char t = op.top();
            op.pop();
            op1.push(t);
        }
        
        while(!num.empty())
        {
            int t = num.top();
            num.pop();
            num1.push(t);
        }
        
        while(!op1.empty())
        {
            char t = op1.top();
            op1.pop();
            long a = num1.top();
            num1.pop();
            long b = num1.top();
            num1.pop();
            num1.push(getNum(a,b,t));
        }
        
        return num1.top();
    }
};

起加減