“计算 24”是一个流传已久的数字游戏，小蓝最近对此痴迷不已。
游戏规则是：对 4 个 1-10 之间的自然数，进行加、减、乘三种运算，要求运算结果等于 24。乘法的优先级高于加、减，并且算式中不可以用括号，不可以改变 4 个数字出现的顺序。
下面我们给出两个游戏的具体例子：
若给出的 4 个操作数是：10、2、4、8，则有两种可能的解答方案：
10+2+4+8=24，10*2-4+8=24，输出内容：2
若给出的 4 个操作数是：7、2、3、6，则没有解答案，输出内容：0。
对于此题：大家应该暴力写代码都会了，但是本人在这里是要介绍简写代码的方法。
1.复制法：
首先，先写下以上代码：
if (a + b + c + d == 24 ) sum ++;
if (a + b + c - d == 24 ) sum ++;
if (a + b + c * d == 24 ) sum ++;
if (a + b - c + d == 24 ) sum ++;
if (a + b - c - d == 24 ) sum ++;
if (a + b - c * d == 24 ) sum ++;
if (a + b * c + d == 24 ) sum ++;
if (a + b * c - d == 24 ) sum ++;
if (a + b * c * d == 24 ) sum ++;再把每组中的第一个“+”号，分别改成减号和乘号就欧啦。
2.代码法：
作为一个懒人，连复制都懒得复制了。
于是呼：用代码帮我们写代码。
首先：先打开另一个c++文件，插入以下代码：
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define MAXN 1048586
#define M 1005
#define N 500005
#define lowbit(x) ((x)&(-(x)))
#define debug(...) cout << '[' << 'D' << 'E' << ']' << ' ' << __LINE__ << ':' << __VA_ARGS__ << endl;
#define vl(x) #x << '(' << x << ')'
#define mod 998244353
#define who(s,limit,tpe) s + tpe , s + limit + tpe
#define all(s) s.begin(),s.end()
#define s_(s) s.size()
int a[N];
string s[M] = {"","+++","++-","++*","+-+","+--","+-*","+*+","+*-","+**","-++","-+-","-+*","--+","---","--*","-*+","-*-","-**","*++","*+-","*+*","*-+","*--","*-*","**+","**-","***"};
vector<int> G[N];
int main(){
int n;
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
for(int i = 1; i <= 27; i ++){
cout << " " << "if (a " << s[i][0] << " b " << s[i][1] << " c " << s[i][2] << " d == 24 ) sum ++;" << endl ;
}
}你会惊奇的发现：输出的代码竟是我们需要的代码！
我们要多利用代码帮我们写代码，做到多偷懒。^_^
// 输出
if (a + b + c + d == 24 ) sum ++;
if (a + b + c - d == 24 ) sum ++;
if (a + b + c * d == 24 ) sum ++;
if (a + b - c + d == 24 ) sum ++;
if (a + b - c - d == 24 ) sum ++;
if (a + b - c * d == 24 ) sum ++;
if (a + b * c + d == 24 ) sum ++;
if (a + b * c - d == 24 ) sum ++;
if (a + b * c * d == 24 ) sum ++;
if (a - b + c + d == 24 ) sum ++;
if (a - b + c - d == 24 ) sum ++;
if (a - b + c * d == 24 ) sum ++;
if (a - b - c + d == 24 ) sum ++;
if (a - b - c - d == 24 ) sum ++;
if (a - b - c * d == 24 ) sum ++;
if (a - b * c + d == 24 ) sum ++;
if (a - b * c - d == 24 ) sum ++;
if (a - b * c * d == 24 ) sum ++;
if (a * b + c + d == 24 ) sum ++;
if (a * b + c - d == 24 ) sum ++;
if (a * b + c * d == 24 ) sum ++;
if (a * b - c + d == 24 ) sum ++;
if (a * b - c - d == 24 ) sum ++;
if (a * b - c * d == 24 ) sum ++;
if (a * b * c + d == 24 ) sum ++;
if (a * b * c - d == 24 ) sum ++;
if (a * b * c * d == 24 ) sum ++;所以，代码为：
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define MAXN 1048586
#define M 1005
#define N 500005
#define lowbit(x) ((x)&(-(x)))
#define debug(...) cout << '[' << 'D' << 'E' << ']' << ' ' << __LINE__ << ':' << __VA_ARGS__ << endl;
#define vl(x) #x << '(' << x << ')'
#define mod 998244353
#define who(s,limit,tpe) s + tpe , s + limit + tpe
#define all(s) s.begin(),s.end()
#define s_(s) s.size()
int a[N];
string s;
vector<int> G[N];
int main(){
int n;
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int a,b,c,d;
cin >> a >> b >> c >> d;
int sum = 0 ;
if (a + b + c + d == 24 ) sum ++;
if (a + b + c - d == 24 ) sum ++;
if (a + b + c * d == 24 ) sum ++;
if (a + b - c + d == 24 ) sum ++;
if (a + b - c - d == 24 ) sum ++;
if (a + b - c * d == 24 ) sum ++;
if (a + b * c + d == 24 ) sum ++;
if (a + b * c - d == 24 ) sum ++;
if (a + b * c * d == 24 ) sum ++;
if (a - b + c + d == 24 ) sum ++;
if (a - b + c - d == 24 ) sum ++;
if (a - b + c * d == 24 ) sum ++;
if (a - b - c + d == 24 ) sum ++;
if (a - b - c - d == 24 ) sum ++;
if (a - b - c * d == 24 ) sum ++;
if (a - b * c + d == 24 ) sum ++;
if (a - b * c - d == 24 ) sum ++;
if (a - b * c * d == 24 ) sum ++;
if (a * b + c + d == 24 ) sum ++;
if (a * b + c - d == 24 ) sum ++;
if (a * b + c * d == 24 ) sum ++;
if (a * b - c + d == 24 ) sum ++;
if (a * b - c - d == 24 ) sum ++;
if (a * b - c * d == 24 ) sum ++;
if (a * b * c + d == 24 ) sum ++;
if (a * b * c - d == 24 ) sum ++;
if (a * b * c * d == 24 ) sum ++;
cout << sum << endl ;
}The End.
