算法参考链接链接

#include<iostream>
#include<algorithm>
#include<cstring>
#include<stack>
#include<unordered_map>

using namespace std;

stack<string> num;
stack<char> op;

string str;

int main()
{
    unordered_map<char, int> pr{ {'(', 0}, {'+', 1}, {'-', 1}, {'*', 2},{'/', 2} };
    cin >> str;
    int n = str.size();
    for (int i = 0; i < n; i++) 
    {
        char c = str[i];
        if (isdigit(c))
        {
            int x = 0, j = i;
            while (j < n && isdigit(str[j]))
            {
                x = x * 10 + str[j++] - '0';
            }
            i = j - 1;
            num.push(to_string(x));
        }
        else
        {
            if (c == '(') op.push(c);
            else if (c == ')')
            {
                while (op.top() != '(') 
                {
                    string s(1, op.top());
                    num.push(s);
                    op.pop();
                }
                op.pop();
            }
            else if (op.empty() || pr[op.top()] < pr[c]) op.push(c);
            else
            {
                while (op.size() && pr[op.top()] >= pr[c])
                {
                    string s(1, op.top());
                    num.push(s);
                    op.pop();
                }
                op.push(c);
            }
        }
    }
    while (op.size())
    {
        string s(1, op.top());
        num.push(s);
        op.pop();
    }
    vector<string> v;
    while (num.size())
    {
        v.push_back(num.top());
        num.pop();
    }
    for (int i = v.size() - 1; i >= 0; i--) cout << v[i] << " ";
    return 0;
}