BM49 表达式求值

#include <iostream>
#include <string>
#include <stack>
using namespace std;
static inline int GetPrecendence(const char &c){
    switch(c){
    case '+':
    case '-':
        return 10;
    case '*':
    case '/':
        return 20;
    default:
        return 0;
    }
}
static inline bool IsNum(const char &c){
    return c>='0'&&c<='9';
}
static inline bool IsOp(const char &c){
    bool ret=false;
    if(c=='+'||c=='-'||c=='*'||c=='/'){
        ret=true;
    }
    return ret;
}
static inline bool IsTerminator(const char &c){
    bool ret=false;
    if(IsOp(c)||'('==c||')'==c){
        ret=true;
       }
    return ret;
}
static inline int Cal(const int &a,const int&b,const char& op){
    std::cout<<a<<" "<<b<<" "<<op<<std::endl;
    switch(op){
    case '+':
        return a+b;
    case '-':
        return a-b;
    case '*':
        return a*b;
    case '/':
        return a/b;
    default:
        return 0;
    }
}
class Solution {
public:
    int solve(string s) {
        // write code here
        int n=s.size();
        int i=0;
        int val=0;
        bool num_flag=false;
        while(i<n){
            if(IsNum(s[i])){
                val=val*10+s[i]-'0';
                num_flag=true;
            }
            if(i==n-1||IsTerminator(s[i])){
                if(num_flag){
                    std::cout<<val<<std::endl;
                    nums.push(val);
                }
                val=0;
                num_flag=false;
            }
            if('('==s[i]){
                ops.push(s[i]);
               }else if(')'==s[i]){
                    while('('!=ops.top()){
                        int r=0;
                        int right=nums.top();
                        nums.pop();
                        char op=ops.top();
                        ops.pop();
                        if(IsOp(op)){
                            int left=nums.top();
                            nums.pop();
                            r=Cal(left,right,op);
                        }else{
                            r=right;
                        }
                        nums.push(r);
                    }
                    ops.pop();
               }else if(IsOp(s[i])){
                    if(ops.empty()||'('==s[i]){
                        ops.push(s[i]);
                    }else if(IsOp(ops.top())&&GetPrecendence(ops.top())>=GetPrecendence(s[i])){
                        int right=nums.top();
                        nums.pop();
                        int left=nums.top();
                        nums.pop();
                        char op=ops.top();
                        ops.pop();
                        int r=Cal(left,right,op);
                        nums.push(r);
                        ops.push(s[i]);
                    }else{
                        ops.push(s[i]);
                    }
               }
            i++;
        }
        while(!ops.empty()){
            int right=nums.top();
            nums.pop();
            int left=nums.top();
            nums.pop();
            char op=ops.top();
            ops.pop();
            int r=Cal(left,right,op);
            nums.push(r);
        }
        int r=0;
        r=nums.top();
        nums.pop();
        return r;
}
private:
    std::stack<char> ops;
    std::stack<int> nums;
};
int main(){
    std::string expression="1 2 +2 + (2+2+1*2)*3";
    Solution so;
    int r=so.solve(expression);
    std::cout<<r<<std::endl;
    return 0;
}

[1] BM49 表达式求值-中等