poj 1579 Function Run Fun

#include <iostream>
using namespace std;

int rec[21][21][21];
int w(int a,int b,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(rec[a][b][c]!=-1)
        return rec[a][b][c];
    else
    {
        int s;
        if(a<b&&b<c)
            s=w(a,b,c-1)+w(a,b-1,c-1)-w(a,b-1,c);
        else
            s=w(a-1,b,c)+w(a-1,b-1,c)+w(a-1,b,c-1)-w(a-1,b-1,c-1);
        rec[a][b][c]=s;
        return s;
    }
}
int main()
{    
    int a,b,c;
    memset(rec,-1,sizeof(rec));
    while(cin>>a>>b>>c)
    {
        if(a==-1&&b==-1&&c==-1)
            break;
        printf("w(%d, %d, %d) = %d\n",a,b,c,w(a,b,c));
    }
    return 0;
}