测试数据结果一样，为啥WA

#include <iostream>
using namespace std;
int f[25][25][25];

int fun(int a, int b, int c) {
	if (a <= 0 || b <= 0 || c <= 0)
		return 1;
	else if (a > 20 || b > 20 || c > 20)
		return fun(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] = fun(a, b, c - 1) + fun(a, b - 1, c - 1) - fun(a, b - 1, c);
	else
		f[a][b][c] = fun(a - 1, b, c) + fun(a - 1, b - 1, c) + fun(a - 1, b, c - 1) - fun(a - 1, b - 1, c - 1);
	return f[a][b][c];
}

int main() {
	while (1) {
		int a, b, c;
		cin >> a >> b >> c;
		if (a == -1 && b == -1 && c == -1)
			break;
		cout << "fun(" << a << ", " << b << ", " << c << ") = " << fun(a, b, c) << endl;
	}
}