poj 3295 Tautology 伪递归

 1 #include <cstdio>//本代码用G++交就ac，c++交就wa，因为G++是从前向后求值的，c++是从后向前求值的，
 2 #include <cstring>
 3 #include <cstdlib>
 4 #include <iostream>
 5 #include <algorithm>
 6 using namespace std;
 7 #define maxn 105
 8 char str[maxn];
 9 int index;
10 
11 bool dfs (int num);//对表达式求值
12 bool judge ();//对变量的取值进行枚举
13 int main ()
14 {
15     while (scanf ("%s", str), strcmp(str, "0"))
16     {
17         if (judge ())
18             printf ("tautology\n");
19         else
20             printf ("not\n");
21     }
22     return 0;
23 }
24 bool dfs (int num)
25 {
26     index ++;
27     if (str[index] == ‘p‘)
28         return num & 1;
29     else if (str[index] == ‘q‘)
30         return (num >> 1) & 1;
31     else if (str[index] == ‘r‘)
32         return (num >> 2) & 1;
33     else if (str[index] == ‘s‘)
34         return (num >> 3) & 1;
35     else if (str[index] == ‘t‘)
36         return (num >> 4) & 1;
37     else if (str[index] == ‘K‘)
38         return dfs (num) & dfs (num);//这里的& | 不能用&& ||，因为后者使用时前面的为假就会停止运算，不能达到预计的效果
39     else if (str[index] == ‘A‘)
40         return dfs (num) | dfs (num);
41     else if (str[index] == ‘N‘)
42         return !dfs (num);
43     else if (str[index] == ‘C‘)
44         return !dfs(num) | dfs(num);
45     else if (str[index] == ‘E‘)
46         return dfs (num) == dfs(num);
47 
48 }
49 bool judge ()
50 {
51     int i;
52     for (i=0; i<32; i++)
53     {
54         index = -1;
55         if (!dfs (i))
56             return 0;
57     }
58     return 1;
59 }