HDU 1331（Function Run Fun）

直接暴力打表即可。

#include <iostream>
using namespace std;
const int MAXN = 25;

int f[MAXN][MAXN][MAXN]; //记录w(a,b,c)

//计算w(a,b,c)
void w(int a, int b, int c)
{
    if (a <= 0 || b <= 0 || c <= 0)
        f[a][b][c] = 1;
    else if (a < b && b < c)
        f[a][b][c] = f[a][b][c - 1] + f[a][b - 1][c - 1] - f[a][b - 1][c];
    else
        f[a][b][c] = f[a - 1][b][c] + f[a - 1][b - 1][c] + f[a - 1][b][c - 1] - f[a - 1][b - 1][c - 1];
}

int main()
{
    for (int i = 0; i <= 20; i++) //打表
    {
        for (int j = 0; j <= 20; j++)
            for (int k = 0; k <= 20; k++)
                w(i, j, k);
    }

    int a, b, c;
    while (cin >> a >> b >> c)
    {
        if (a == -1 && b == -1 && c == -1)
            break;

        cout << "w(" << a << ", " << b << ", " << c << ") = ";
        if (a <= 0 || b <= 0 || c <= 0)
            cout << 1 << endl;
        else if (a > 20 || b > 20 || c > 20)
            cout << f[20][20][20] << endl;
        else
            cout << f[a][b][c] << endl;
    }
    return 0;
}

继续加油。