[CCF] 201903-2 二十四点

题面

思路：计算中缀表达式，然后判断24即可

我的代码

//CCF 201903-2 二十四点 
#include <bits/stdc++.h>
using namespace std;
char str[10],in[20];
int a[10]; 
int super(char ch)
{
	if(ch=='+'||ch=='-') return 2;
	if(ch=='x'||ch=='/'||ch=='*') return 3;
	if(ch=='#') return 0;
	return -1; 
}
int cal(int x,int y,char op)
{
	if(op=='+') return x+y;
	else if(op=='-') return x-y;
	else if(op=='/') return x/y;
	else return x*y;	
} 
void solve()
{	
	stack<int> num;
	stack<char> alp;
	alp.push('#');
	for(int i=0;i<7;++i)
	{
		if(isdigit(in[i]))	
		{
			num.push(in[i]-'0');
		}
		else
		{
			char now = in[i];
			while(super(now)<=super(alp.top()))
			{
				char tp = alp.top();   alp.pop();
				int right = num.top(); num.pop();
				int left  = num.top(); num.pop();
				num.push(cal(left,right,tp));
			}
			alp.push(now);
		} 
	} 
	while(!alp.empty()&&alp.top()!='#')
	{
		char tp = alp.top();
		alp.pop();
		int right = num.top();num.pop();
		int left  = num.top();num.pop();
		num.push(cal(left,right,tp));
	}
	if(num.top()==24) puts("Yes");
	else puts("No");
}
int main()
{
	int T;cin>>T;
	while(T--)
	{
		scanf("%s",in); 
		solve();
	}
	
	return 0;	
}