P1464 Function

题目传送门

#include <bits/stdc++.h>

using namespace std;
const int N = 25;
typedef long long LL;

LL f[N][N][N];

LL w(LL a, LL b, LL c) {
    //注意判断的顺序，防止数组下标越界出现RE错误
    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]) return f[a][b][c];
    else if (a < b && b < c) f[a][b][c] = w(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() {
    LL 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;
}