样例是对的，也不会爆（应该

代码如下：：：：：：：

#include <iostream>
using namespace std;
long long x, y, z, r[25][25][25];
long long func(long long a, long long b, long long c){
	if(a <= 0 || b <= 0 || c <= 0){
		return 1;
	} else if(r[a][b][c] != 0){
		return r[a][b][c];
	} else if(a > 20 || b > 20 || c > 20){
		r[a][b][c] = func(20, 20, 20);
	} else if(a < b && b < c){
		r[a][b][c] = func(a, b, c - 1) + func(a, b - 1, c - 1) - func(a, b - 1, c);
	} else{
		r[a][b][c] = func(a - 1, b, c) + func(a - 1, b - 1, c) + func(a - 1, b, c - 1) - func(a - 1, b - 1, c - 1);
	}
}
int main() {
	cin >> x >> y >> z;
	while(x != -1 && y != -1 && z != -1){
		if(x > 20) x = 21;
		if(y > 20) y = 21;
		if(z > 20) z = 21;
		cout << "w(" << x << ", " << y << ", " << z << ") = " << func(x, y, z) << endl;
		cin >> x >> y >> z;
	}
    return 0;
}