3360: [Usaco2004 Jan]算二十四

 1 const d:array[1..3] of char=('+','-','*');
 2 var
 3         i,j,k,l,m,n:longint;
 4         a,b:array[0..20] of longint;
 5 function calc:int64;
 6         var i:longint;a1,a2,a3:int64;
 7         begin
 8                 a1:=0;a2:=a[1];a3:=1;
 9                 for i:=2 to n do
10                         begin
11                                 case b[i-1] of
12                                         1:BEGIN
13                                                 if a3=1 then a1:=a1+a2 else a1:=a1-a2;
14                                                 a2:=a[i];a3:=1;
15                                         end;
16                                         2:begin
17                                                 if a3=1 then a1:=a1+a2 else a1:=a1-a2;
18                                                 a2:=a[i];a3:=2;
19                                         end;
20                                         3:begin
21                                                 a2:=a2*a[i];
22                                         end;
23                                 end;
24                         end;
25                 if a3=1 then a1:=a1+a2 else a1:=a1-a2;
26                 calc:=a1;
27         end;
28 procedure dfs(x:longint);inline;
29         var i:longint;
30         begin
31                 if x>=n then
32                         begin
33                                 if calc=24 then inc(l);
34                                 exit;
35                         end;
36                 for i:=1 to 3 do
37                         begin
38                                 b[x]:=i;
39                                 dfs(x+1);
40                         end;
41         end;
42 begin
43         readln(n);
44         for i:=1 to n do readln(a[i]);
45         l:=0;
46         dfs(1);
47         writeln(l);
48 end.