记忆化搜索--Function Run Fun

Function Run Fun

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

代码 

#include
#include
#include 
#include
#include
#include
#include
#include
#include

 using namespace std;

 int m[25][25][25]={0};
int w(int a,int b,int c)
{
    if(a<=0||b<=0||c<=0)
        return 1;
    if(a>20||b>20||c>20)//先判断大于二十的情况就不用定义太大的数组
        return w(20,20,20);
     if(m[a][b][c])//避免重复计算已知的的数，减少时间损耗
        return m[a][b][c];
     if(a>a>>b>>c)//while循环
    {
        if(a==-1&&b==-1&&c==-1)//满足条件退出
            break;
         d=w(a,b,c);
    printf("w(%d, %d, %d) = %d\n",a,b,c,d);//一定注意输出格式！！！！！！
    }

    return 0;
}