POJ 1579 Function Run Fun

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<stack>
#include<queue>
#include<cmath>
using namespace std;
int dp[21][21][21];
int recursion(int a,int b,int c)
{
if(a<=0||b<=0||c<=0)
return 1;
if(dp[a][b][c]>=0)
return dp[a][b][c];
int res=0;
if(a<b&&b<c)
res=recursion(a,b,c-1)+recursion(a,b-1,c-1)-recursion(a,b-1,c);
else
res=recursion(a-1,b,c)+recursion(a-1,b-1,c)+recursion(a-1,b,c-1)-recursion(a-1,b-1,c-1);
return dp[a][b][c]=res;
}
int main()
{
int a,b,c;
while(scanf("%d%d%d",&a,&b,&c))
{
if(a==-1&&b==-1&&c==-1)
break;
memset(dp,-1,sizeof(dp));
int ans=0;
if(a<=0||b<=0||c<=0)
ans=1;
else if(a>20||b>20||c>20)
ans=recursion(20,20,20);
else
ans=recursion(a,b,c);
printf("w(%d, %d, %d) = %d\n",a,b,c,ans);
}
return 0;
}