题解 | 四则运算

参考别人的

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


int priority(char c)
{
    if(c == '+' ||  c=='-')
    {
        return 111;
    }
    if(c == '*' ||  c=='/')
    {
        return 222;
    }
    return 0;
}

string normalize(string s)
{
    for(int i=0; i<s.length(); i++)
    {
        if(s[i] == '[') s[i] = '(';
        if(s[i] == '{') s[i] = '(';
        if(s[i] == ']') s[i] = ')';
        if(s[i] == '}') s[i] = ')';
    }
    return s;
}

int apply_calc(int a, int b, char op)
{
    int result ;
    switch (op) {
        case '+':
            result = a+b;
            break;
        case '-':
            result = a-b;
            break;
        case '*':
            result = a*b;
            break;
        case '/':
            result = a/b;
            break;
    }

    return result;
}

void calc(stack<char>& ops, stack<int>& nums)
{
    int b = nums.top(); nums.pop();
    int a = nums.top(); nums.pop();
    char op = ops.top(); ops.pop();
    nums.push(apply_calc(a, b , op));
}

int compute(string& s)
{
    stack<char> Ops;
    stack<int> Nums;
    int n = s.length();
    for(int i=0; i<n; i++)
    {
        if(s[i]=='-' && (i==0 || s[i-1] == '('))
        {
            int number = 0;
            int j=i+1;
            bool is_Number = false;
            while(j<n && isdigit(s[j]))
            {
                is_Number=true;
                number = number*10 + (s[j] - '0');
                j++;
            }
            if(is_Number)
                Nums.push(-1*number);
            i = j;
        }

        else if(isdigit(s[i]))
        {
            int j = i;
            int number = 0;
            while(j < n && isdigit(s[j]))
            {
                number = number * 10 + s[j] - '0';
                j++;
            }
            Nums.push(number);
            i = j;
        }

        if(s[i] == '(')
        {
            Ops.push(s[i]);
        }
        else if(s[i] == ')')
        {
            while(Ops.empty()==false && Ops.top() != '(')
            {
                calc(Ops, Nums);
            }
            if(!Ops.empty())
                Ops.pop();
        }   
        else//operator
        {
            while(Ops.empty()==false && priority(Ops.top()) >= priority(s[i]))
            {
                calc(Ops, Nums);
            }
            Ops.push(s[i]);
        }
    }
    while(Ops.empty() == false && Nums.size() != 1)
    {
        calc(Ops, Nums);
    }
    return Nums.top();
}



int main() 
{
    std::string str;
    getline(cin, str);
  
    str = normalize(str);
    int res = compute(str);
    cout << res;
}