• Tautology


    WFF 'N PROOF is a logic game played with dice. Each die has six faces representing some subset of the possible symbols K, A, N, C, E, p, q, r, s, t. A Well-formed formula (WFF) is any string of these symbols obeying the following rules:

    • p, q, r, s, and t are WFFs
    • if w is a WFF, Nw is a WFF
    • if w and x are WFFs, Kwx, Awx, Cwx, and Ewx are WFFs.

    The meaning of a WFF is defined as follows:

    • p, q, r, s, and t are logical variables that may take on the value 0 (false) or 1 (true).
    • K, A, N, C, E mean and, or, not, implies, and equals as defined in the truth table below.
    Definitions of K, A, N, C, and E
         w  x   Kwx   Awx    Nw   Cwx   Ewx
      1  1   1   1    0   1   1
      1  0   0   1    0   0   0
      0  1   0   1    1   1   0
      0  0   0   0    1   1   1

    A tautology is a WFF that has value 1 (true) regardless of the values of its variables. For example, ApNp is a tautology because it is true regardless of the value of p. On the other hand, ApNq is not, because it has the value 0 for p=0, q=1.

    You must determine whether or not a WFF is a tautology.

    Input

    Input consists of several test cases. Each test case is a single line containing a WFF with no more than 100 symbols. A line containing 0 follows the last case.

    Output

    For each test case, output a line containing tautology or not as appropriate.

    Sample Input

    ApNp
    ApNq
    0

    Sample Output

    tautology
    not

    就是离散数学的一个模拟,判断所给的式子是不是永真公式
    用栈逆序推还不算难
     1 #include<stdio.h>
     2 #include<iostream>
     3 #include<string.h>
     4 #include<stack>
     5 using namespace std;
     6 stack<int>sta;
     7 int p,q,r,s,t,a,b;
     8 char str[102];
     9 int f()
    10 {
    11     int len=strlen(str);
    12     for(int i=len-1; i>-1; i--)
    13     {
    14         if(str[i]=='p')sta.push(p);//是字符直接入栈
    15         else if(str[i]=='q')sta.push(q);
    16         else if(str[i]=='r')sta.push(r);
    17         else if(str[i]=='s')sta.push(s);
    18         else if(str[i]=='t')sta.push(t);
    19         else if(str[i]=='K')//是运算就进行运算
    20         {
    21             a=sta.top();
    22             sta.pop();
    23             b=sta.top();
    24             sta.pop();
    25             sta.push(a&&b);
    26         }
    27         else if(str[i]=='A')
    28         {
    29             a=sta.top();
    30             sta.pop();
    31             b=sta.top();
    32             sta.pop();
    33             sta.push(a||b);
    34         }
    35         else if(str[i]=='C')
    36         {
    37             a=sta.top();
    38             sta.pop();
    39             b=sta.top();
    40             sta.pop();
    41             if(a&&!b)sta.push(0);
    42             else sta.push(1);
    43         }
    44         else if(str[i]=='E')
    45         {
    46             a=sta.top();
    47             sta.pop();
    48             b=sta.top();
    49             sta.pop();
    50             if(a==b)sta.push(1);
    51             else sta.push(0);
    52         }
    53         else if(str[i]=='N')
    54         {
    55             a=sta.top();
    56             sta.pop();
    57             sta.push(!a);
    58         }
    59     }
    60     return sta.top();
    61 }
    62 int sf()//枚举各种情况
    63 {
    64     for(p=0; p<2; p++)
    65         for(q=0; q<2; q++)
    66             for(r=0; r<2; r++)
    67                 for(s=0; s<2; s++)
    68                     for(t=0; t<2; t++)
    69                         if(!f())
    70                             return 0;
    71     return 1;
    72 }
    73 int main()
    74 {
    75     while(gets(str))
    76     {
    77         if(!strcmp(str,"0"))
    78             break;
    79         else
    80         {
    81             if(sf())
    82                 printf("tautology
    ");
    83             else
    84                 printf("not
    ");
    85         }
    86     }
    87     return 0;
    88 }
    View Code
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  • 原文地址:https://www.cnblogs.com/kongkaikai/p/3241838.html
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