ACM学习历程——POJ3295 Tautology（搜索，二叉树）

Description

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


考虑到运算符最多是二元的，将运算符和变量存进二叉树中，结构体中用一个val值来记录是否是变量，为了提高效率，用一个visit数组来记录用到了哪几个变量。此外在最后进行运算的时候，需要二叉树进行后序遍历。此外输入采用先序遍历。


代码：

#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cstring>

#include <cmath>

#include <algorithm>

#include <set>

#include <map>

#include <vector>

#include <queue>

#include <string>

#define inf 0x3fffffff

#define eps 1e-10



using namespace std;



struct node

{

    char op;

    int val;

    node *left;

    node *right;

};



bool a[5];

bool visit[5];



int Do(char op, int x, int y)

{

    switch (op)

    {

        case 'K':

            return x&&y;

        case 'A':

            return x||y;

        case 'N':

            return !x;

        case 'C':

            return !x || y;

        case 'E':

            return x == y;

    }

}



bool Input(node *p)

{

    char ch;

    ch = getchar();

    if (ch == '0')

        return 0;

    p->op = ch;

    p->val = -1;

    switch (ch)

    {

        case 'p':

            p->val = 0;

            visit[0] = 1;

            return 1;

        case 'q':

            p->val = 1;

            visit[1] = 1;

            return 1;

        case 'r':

            p->val = 2;

            visit[2] = 1;

            return 1;

        case 's':

            p->val = 3;

            visit[3] = 1;

            return 1;

        case 't':

            p->val = 4;

            visit[4] = 1;

            return 1;

        case 'N':

            p->left = (node *)malloc(sizeof(node));

            return Input(p->left);

        default:

            p->left = (node *)malloc(sizeof(node));

            p->right = (node *)malloc(sizeof(node));

            Input(p->left);

            return Input(p->right);

    }

}



bool caculate(node *p)

{

    if (p->val != -1)

        return a[p->val];

    if (p->op == 'N')

        return Do(p->op, caculate(p->left), 1);

    else

        return Do(p->op, caculate(p->left), caculate(p->right));

}



bool dfs(int now, node *head)

{

    if (now == 5)

        return caculate(head);

    if (visit[now] == 0)

        return dfs(now+1, head);

    int ii, jj;

    a[now] = 0;

    ii = dfs(now+1, head);

    a[now] = 1;

    jj = dfs(now+1, head);

    return ii && jj;

}



bool qt(node *head)

{

    if (dfs(0, head))

        printf("tautology\n");

    else

        printf("not\n");

}



int main()

{

    //freopen("test.txt", "r", stdin);

    node *head;

    for (;;)

    {

        memset(visit, 0, sizeof(visit));

        head = (node *)malloc(sizeof(node));

        if(!Input(head))

            break;

        getchar();

        qt(head);

    }

    return 0;

}