我甚至跟书上敲的一摸一样了，还是全WA

#include <iostream>
using namespace std;
long long int f[25][25][25];
long long int w(long long int a, long long int b, long long int c) {
	if (a <= 0 || b <= 0 || c <= 0) return 1;
	else if (a > 20 || b > 20 || c > 20) return w(20, 20, 20);
	else if (f[a][b][c] !=  0) return f[a][b][c];
	else if (a < b && b < c)
		f[a][b][c] = (a, b, c - 1) + w(a, b - 1, c - 1) - w(a, b - 1, c);
	else
		f[a][b][c] = w(a - 1, b, c) + w(a - 1, b - 1, c) + w(a - 1, b, c - 1) - w(a - 1, b - 1, c - 1);
	return f[a][b][c];
}
int main() {
	long long int a, b, c;
	while (cin >> a >> b >> c) {
		if (a == -1 && b == -1 && c == -1)
			break;
		cout << "w(" << a << ", " << b << ", " << c << ") = ";
		cout << w(a, b, c) << endl;
	}
	return 0;
}