Basic Calculator（C++基本计算器）

- 日理万妓 2023-01-13 09:47 125阅读 0赞

解题思路：

（1）双栈，前导0

class Solution {
    private:
        bool next_is_op=false;
    public:
        void cal(stack<double> &sd,stack<char> &st) {
            double b=sd.top();
            sd.pop();
            double a=sd.top();
            sd.pop();
            char oper=st.top();
            st.pop();
            if(oper=='+') a=a+b;
            else if(oper=='-') a=a-b;
            else if(oper=='*') a=a*b;
            else if(oper=='/') a=a/b;
            sd.push(a);
            return;
        }
        
        bool cmp(char c1,char  c2) {
            if(c1=='(') return false;
            else if((c1=='+' || c1=='-') && (c2=='*' || c2=='/')) return false;
            return true;
        }
    
        string get(string s) {
            string str="";
            for(int i=0;i<s.length();i++) {
                if(s[i]!=' ') str+=s[i];
            }
            return str;
        }
    
        int calculate(string s) {
            s=get(s);
            if(s[0]=='-' || s[0]=='+') s='0'+s; //前导0
            s='('+s;
            s=s+')';
            stack<double> sd;
            stack<char> st;
            
            for(int i=0;i<s.length();i++) {
                if(s[i]=='(' || s[i]=='[' || s[i]=='{') st.push('(');
                else if(s[i]==')' || s[i]==']' || s[i]=='}') {
                    while(st.top()!='(') cal(sd,st);
                    st.pop();
                } else if(next_is_op) {
                    while(cmp(st.top(),s[i])) cal(sd,st);
                    st.push(s[i]);
                    next_is_op=false;
                } else {
                    int j=i;
                    if(s[i]=='-' || s[i]=='+') i++;
                    while(isdigit(s[i])) i++;
                    double d=double(stoi(s.substr(j,i-j)));
                    sd.push(d);
                    i--;
                    next_is_op=true;
                }
            }
            return sd.top();
        }
    };