LeetCode 227. Basic Calculator II(后缀表达式)

class Solution {
public:
    int s1[1000005];
    int s2[1000005];
    int s3[1000005];
    int top1;
    int top2;
    int top3;
    int calculate(string s) {
        
        top1=0;top2=0;top3=0;
        string str="";
        for(int i=0;i<s.length();i++)
        {
            if(s[i]>='0'&&s[i]<='9')
            {
                str+=s[i];
                continue;
            }
            
            if(str!="")
            {
                s2[top2++] = atoi(str.c_str());
                str="";
            }
            if(s[i]==' ') continue;
            
            if(s[i]=='+'||s[i]=='-'||s[i]=='*'||s[i]=='/')
            {
                if(top1==0)
                {
                    s1[top1++]=change(s[i]);
                }
                else
                {
                    while(top1>=1&&judge(change2(s1[top1-1]),s[i]))
                    {
                        
                        s2[top2++]=s1[top1-1];
                        top1--;
                    }
                    s1[top1++]=change(s[i]);
                } 
            }
        }
        
        if(str!="")
            s2[top2++]=atoi(str.c_str());
        
        while(top1!=0)
        {
            s2[top2++]=s1[top1-1];
            top1--;
        }
        
        for(int i=0;i<top2;i++)
        {
            if(s2[i]==-1)
            {
                int x =s3[top3-2]/s3[top3-1];
                top3-=2;
                s3[top3++]=x;
            }
            else if(s2[i]==-2)
            {
                int x =s3[top3-2]*s3[top3-1];
                top3-=2;
                s3[top3++]=x;
            }
            
            else if(s2[i]==-3)
            {
                int x =s3[top3-2]-s3[top3-1];
                top3-=2;
                s3[top3++]=x;
            }
            
             else if(s2[i]==-4)
            {
                int x =s3[top3-2]+s3[top3-1];
                top3-=2;
                s3[top3++]=x;
            }
            else
            {
                s3[top3++]=s2[i];
            }
        }
        
        return s3[0];
        
    }
    
    int change(char x)
    {
        if(x=='+')
            return -4;
        else if(x=='-')
            return -3;
        else if(x=='*')
            return -2;
        else
            return -1;
    }
    
    char change2(int x)
    {
        if(x==-1)
            return '/';
        else if(x==-2)
            return '*';
        else if(x==-3)
            return '-';
        else
            return '+';
        
    }
    
    int judge(char x,char y)
    {
        if(x=='+'||x=='-')
        {
            if(y=='+'||y=='-')
                return 1;
            if(y=='*'||y=='/')
                return 0;
        }
        
        if(x=='*'||x=='/')
        {
            if(y=='+'||y=='-')
                return 1;
            if(y=='*'||y=='/')
                return 1;
        }
        
        return 0;
    }
};