poj 1579 function run fun

Function Run Fun

Time Limit: 1000MS		Memory Limit: 10000K
Total Submissions: 14985		Accepted: 7758

Description

We all love recursion! Don't we? 

Consider a three-parameter recursive function w(a, b, c): 

if a <= 0 or b <= 0 or c <= 0, then w(a, b, c) returns: 
1 

if a > 20 or b > 20 or c > 20, then w(a, b, c) returns: 
w(20, 20, 20) 

if a < b and b < c, then w(a, b, c) returns: 
w(a, b, c-1) + w(a, b-1, c-1) - w(a, b-1, c) 

otherwise it returns: 
w(a-1, b, c) + w(a-1, b-1, c) + w(a-1, b, c-1) - w(a-1, b-1, c-1) 

This is an easy function to implement. The problem is, if implemented directly, for moderate values of a, b and c (for example, a = 15, b = 15, c = 15), the program takes hours to run because of the massive recursion. 

Input

The input for your program will be a series of integer triples, one per line, until the end-of-file flag of -1 -1 -1. Using the above technique, you are to calculate w(a, b, c) efficiently and print the result.

Output

Print the value for w(a,b,c) for each triple.

Sample Input

1 1 1
2 2 2
10 4 6
50 50 50
-1 7 18
-1 -1 -1

Sample Output

w(1, 1, 1) = 2
w(2, 2, 2) = 4
w(10, 4, 6) = 523
w(50, 50, 50) = 1048576
w(-1, 7, 18) = 1

代碼：

#include<stdio.h>
#include<string.h>


int ans[22][22][22];


int w(int a,int b,int c)
{
	if(a<=0 || b<=0 || c<=0)
		return 1;
	if(a>20 || b>20 || c>20)
		return ans[20][20][20]=w(20,20,20);
	if(ans[a][b][c])
		return ans[a][b][c];
	if(a<b && b<c)
		return ans[a][b][c]=w(a,b,c-1)+w(a,b-1,c-1)-w(a,b-1,c);
	else
		return ans[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);
}
int main()
{
	int a,b,c,res;
	memset(ans,0,sizeof(ans));
	while(scanf("%d %d %d",&a,&b,&c),!(a==-1 && b==-1 && c==-1))
	{
		res=w(a,b,c);
		printf("w(%d, %d, %d) = %d\n",a,b,c,res);
	}
	return 0;
}