题解 | #表达式求值# 简单题？

#include <cctype>
#include <iostream>
using namespace std;
#include <vector>

int compute(string& s, int left, int right) {
    char op = '+';
    int num = 0;
    vector<int> st;//不含运算符的字问题结果
    for (int i = left; i <= right; i++) {
        if (isdigit(s[i])) { //数字
            num = num * 10 + s[i] - '0';
        }
        if (s[i] == '(') { //括号
            int layer = 0;
            int j = i;
            while (j <= right) {
                if (s[j] == '(') {
                    layer++;
                } else if (s[j] == ')') {
                    layer--;
                    if (layer == 0) {
                        break;
                    }
                }              
                j++;//定位到最外层的右括号
            }
            num = compute(s, i + 1, j - 1);
            i = j + 1;          
        }
        if(!isdigit(s[i])||i==right){//运算符或到头了
            switch(op){
                case '+':st.push_back(num);break;
                case '-':st.push_back(-num);break;
                case '*':st.back()*=num;break;
                case '/':st.back()/=num;break;                 
            }
            op=s[i];//更新运算符
            num=0; //清空num
        }        
        
    }
    int res=0;
    for(int n:st){
        res+=n;
    }
    return res;

}
int main() {
    string s;
    while(cin>>s){
        int ans=compute(s, 0, s.size()-1);
        cout<<ans<<endl;
    }
    return 0;
}
// 64 位输出请用 printf("%lld")