中缀表达式转后转表达式

记录一下这个恶心的字符串模拟

#include <bits/stdc++.h>
using namespace std;

int main()
{
    map<char, int> mp;
    string str;
    stack<char> s;
    cin >> str;
    bool isFirst = true;
    mp['-'] = 1, mp['+'] = 1;
    mp['*'] = 2, mp['/'] = 2;
    mp['('] = 3, mp[')'] = 3;
    for (int i = 0; i < str.size(); i++)
    {
        if ((i == 0 || str[i - 1] == '(') && (str[i] == '+' || str[i] == '-') || (str[i] >= '0' && str[i] <= '9') || str[i] == '.') //读入运算数/正负号（区别于加减号）/小数点
        {
            if (!isFirst)
            {
                cout << " ";
            }
            if (str[i] != '+') //省略正号
                cout << str[i];
            while (str[i + 1] == '.' || (str[i + 1] >= '0' && str[i + 1] <= '9')) //处理多位数
            {
                i++;
                cout << str[i];
            }
            isFirst = false;
        }
        else
        {
            if (str[i] == ')') //处理右括号
            {
                while (!s.empty() && s.top() != '(')
                {
                    cout << " " << s.top();
                    s.pop();
                }
                s.pop(); //弹出左括号
            }
            else if (s.empty() || mp[str[i]] > mp[s.top()]) //如果栈空||当前运算符优先级大于栈顶运算符优先级
            {
                s.push(str[i]);
            }
            else //当前运算符优先级小于等于栈顶运算符优先级
            {
                while (!s.empty() && s.top() != '(')
                {
                    cout << " " << s.top();
                    s.pop();
                }
                s.push(str[i]); //将当前运算符压栈
            }
        }
    }
    while (!s.empty()) //将剩余元素弹栈
    {
        cout << " " << s.top();
        s.pop();
    }
}