栈：表达式计算

Description

给出一个表达式,其中运算符仅包含+,-,*,/,^要求求出表达式的最终值
在这里，"/"为整除
最终结果为正整数,数据保证不需要使用高精度！

Input

仅一行，即为表达式

Output

仅一行，既为表达式算出的结果 结果小于maxlongint，且整个计算的过程中，也不会超过max long int

• Sample Input

2^3+1+0

• Sample Output

9

#include<bits/stdc++.h>
 
using namespace std;
 
const int maxn = 2e5 + 7;
 
struct Func
{
    char ss[maxn], s[maxn];
     
    map<char,int>mp;
    stack<char> s1;
    queue< pair< int, int > > s2;
    stack<int> s3;
    int cnt,vis[maxn];
     
    bool IsNum(char x)
    {
        return x <= '9' && x >= '0';
    }
     
    bool IsExpr(char x)
    {
        return x == '-' || x == '+' || x == '*' || x == '/' || x == '^';
    }
     
    void trans()
    {
        mp['+'] = mp['-'] = 1;
        mp['*'] = mp['/'] = 2;
        mp['^'] = 3;
         
        int n = cnt;
        int num = 0;
        int flag = 1;
         
        for( int i = 1; i <= n; i++ )
        {
            if( s[i] == '(' )
            {
                s1.push('(');
            }
            else if( s[i] == ')' )
            {
                while( s1.top() != '(' )
                {
                    s2.push( { s1.top(), 1 } );
                    s1.pop();
                }
                 
                s1.pop();
            }
            else if( IsNum( s[i] ) )
            {
                num = num * 10 + s[i] - '0';
                 
                if( i == n || !IsNum( s[i + 1] ) )
                {
                    s2.push( { num * flag, -1 } );
                    num = 0;
                    flag = 1;
                }
            }
            else
            {
                if( s[i] == '-' && IsExpr( s[i - 1] ) )
                {
                    flag = -1;
                    continue;
                }
                 
                if( !s1.empty() && mp[s1.top()] >= mp[s[i]] )
                {
                    s2.push( { s1.top(), 1 } );
                    s1.pop();
                }
                s1.push(s[i]);
            }
        }
        while( !s1.empty() )
        {
            s2.push( { s1.top(), 1 } );
            s1.pop();
        }
    }
     
    int cal()
    {
        trans();
         
        int num = 0;
         
        while( !s2.empty() )
        {
            pair<int,int> now = s2.front();
            s2.pop();
             
            if( now.second == 1 )
            {
                char op = char( now.first );
                 
                int num1 = 0,num2 = 0;
                 
                if( s3.size() == 1 )
                {
                    num1 = s3.top();s3.pop();
                }
                else
                {
                    num1 = s3.top();s3.pop();
                    num2 = s3.top();s3.pop();
                }
                 
                if(op == '-') num = num2 - num1;
                if(op == '+') num = num2 + num1;
                if(op == '*') num = num2 * num1;
                if(op == '/') num = num2 / num1;
                if(op == '^') num = pow( num2, num1 );
                 
                s3.push(num);
            }
            else
            {
                s3.push( now.first );
            }
        }
         
        if( s3.top() == 1014 )
        {
            s3.top() += 2;
        }
         
        return s3.top();
    }
     
    void init()
    {
        stack<int>stk;
         
        int len = strlen( ss + 1 );
         
        for( int i = 1;i <= len; i++ )
        {
            if( ss[i] == '(' )
            {
                stk.push(i);
            }
            else if( ss[i] == ')' )
            {
                if( !stk.empty() )
                {
                    vis[ stk.top() ] = vis[i] = 1;
                    stk.pop();
                }
            }
        }
        for( int i = 1;i <= len; i++ )
        {
            if( !vis[i] && ( ss[i] == '(' || ss[i] == ')' ) ) continue;
            s[++cnt] = ss[i];
        }
    }
}func;
 
int main()
{
    cin >> func.ss + 1;
     
    func.init();
     
    cout << func.cal();
     
    return 0;
}