const double Threshold = 1E-6;
const int CardsNumber = 4;
const int ResultValue = 24;
double number[CardsNumber];
string result[CardsNumber];
bool PointsGame(int n)
{
if(n == 1)
{
// 由于浮点数运算会有精度误差，所以用一个很小的数1E-6来做容差值
// 本书2.6节中讨论了如何将浮点数转化为分数的问题
if(fabs(number[0] - ResultValue) < Threshold)
{
cout << result[0] << endl;
return true;
}
else
{
return false;
}
}
for(int i = 0; i < n; i++)
{
for(int j = i + 1; j < n; j++)
{
double a, b;
string expa, expb;
a = number[i];
b = number[j];
number[j] = number[n - 1];
expa = result[i];
expb = result[j];
result[j] = result[n - 1];
result[i] = '(' + expa + '+' + expb + ')';
number[i] = a + b;
if(PointsGame(n - 1))
return true;
result[i] = '(' + expa + '-' + expb + ')';
number[i] = a - b;
if(PointsGame(n - 1))
return true;
result[i] = '(' + expb + '-' + expa + ')';
number[i] = b - a;
if(PointsGame(n - 1))
return true;
result[i] = '(' + expa + '*' + expb + ')';
number[i] = a * b;
if(PointsGame(n - 1))
return true;
if(b != 0)
{
result[i] = '(' + expa + '/' + expb + ')';
number[i] = a / b;
if(PointsGame(n - 1))
return true;
}
if(a != 0)
{
result[i] = '(' + expb + '/' + expa + ')';
number[i] = b / a;
if(PointsGame(n - 1))
return true;
}
number[i] = a;
number[j] = b;
result[i] = expa;
result[j] = expb;
}
}
return false;
}
int main()
{
int x;
for(int i = 0; i < CardsNumber; i++)
{
char buffer[20];
cout << "the " << i << "th number:";
cin >> x;
number[i] = x;
itoa(x, buffer, 10);
result[i] = buffer;
}
if(PointsGame(CardsNumber))
{
cout << "Success." << endl;
}
else
{
cout << "Fail." << endl;
}
}
