POJ 1579 解法一常规解法利用数组来解答，较容易想。

 1 #include<stdio.h>
 2 int w[21][21][21];   
 3 int main()
 4 {
 5     int a,b,c;
 6   
 7     for(a=0; a<21; a++)
 8     for(b=0; b<21; b++)
 9      for(c=0; c<21; c++)
10      {
11          if(a<=0||b<=0||c<=0)
12            w[a][b][c] = 1;
13          else if(a<b && b<c)
14            w[a][b][c] = w[a][b][c-1]+w[a][b-1][c-1]-w[a][b-1][c];
15          else
16        w[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];
17       }
18     while(1)
19     {
20        scanf("%d%d%d", &a, &b, &c);
21        if(a==-1 && b==-1 && c==-1) break;
22        printf("w(%d, %d, %d) = ",a,b,c);
23        if(a<=0 || b<=0 || c<=0)
24        {
25            a = 0;
26            b = 0;
27            c = 0;
28        }
29        else if(a>20 || b>20 || c>20)
30        {
31           a = 20;
32           b = 20;
33           c = 20;
34        }
35        
36        printf("%d\n",w[a][b][c]);
37     } 
38   return 0;  
39 }    
40