【发布时间】：2017-05-01 12:44:03
【问题描述】：
我只是在网上找到了这段代码，不明白输入应该如何格式化。来自同一程序员的类似输入示例如下所示：Pushdown automaton implemented in C
但它仍然没有太大帮助。它是这样说的：
输入格式如下： e01:e0$:000111:a:ad:aeeb$:b0eb0:b10ce:c10ce:ce$de 输入是 用分号“:”隔开，第一部分是“输入字母”， 第二个是“堆栈字母”，然后是“输入”，最后一整串是 转换函数。
谁能提供一些如何处理输入的指导？我现在非常努力地努力了大约 6 个小时，但我终其一生都无法破译此代码的输入格式。
使用 gcc 编译后，运行它只需执行“./executable”并按 Enter。然后粘贴如上所示的示例输入字符串（尽管对于这个程序，我需要不同的输入）。
/* This C file implements a Turing Machine
* author: Kevin Zhou
* Computer Science and Electronics
* University of Bristol
* Date: 21st April 2010
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct tapes {
struct tapes *left;
struct tapes *right;
char content;
} Tape;
typedef enum { LEFT,RIGHT } Direction;
typedef struct transition {
char current_state;
char tape_symbol;
char new_state;
char new_tape_symbol;
Direction dir;
} Transition;
typedef struct list {
Transition *content;
struct list *next;
} List;
typedef struct tm {
char *input_alpha;
char *input;
char *tape_alpha;
char start;
char accept;
char reject;
List *transition;
} TM;
Tape *insert_tape(Tape *t, Direction dir, char c) {
Tape *head = t;
Tape *new1 = calloc(1,sizeof(Tape));;
new1 -> content = c;
if(dir == LEFT) {
while(t->left != NULL) {
t = t->left;
}
new1->right = t;
new1->left = NULL;
t->left = new1;
return new1;
}
if(dir == RIGHT) {
while(t->right != NULL) {
t = t->right;
}
new1->left = t;
new1->right = NULL;
t->right = new1;
}
return head;
}
Tape *create_tape(char *input) {
int i=1;
Tape *t = calloc(1,sizeof(Tape));
t->content = input[0];
while(1) {
if(input[i] == '\0') break;
t = insert_tape(t,RIGHT,input[i]);
i++;
}
return t;
}
/* turn the input string into Transition fields */
Transition *get_transition(char *s) {
Transition *t = calloc(1,sizeof(Transition));
Direction dir;
t->current_state = s[0];
t->tape_symbol = s[1];
t->new_state = s[2];
t->new_tape_symbol = s[3];
dir = (s[4]=='R')? RIGHT:LEFT;
t->dir = dir;
return t;
}
/* turn the string into transitions and add into list */
List *insert_list( List *l, char *elem ) {
List *t = calloc(1,sizeof(List));
List *head = l;
while(l->next!=NULL)
l = l->next;
t->content = get_transition(elem);
t->next = NULL;
l->next = t;
return head;
}
/* insert a transition into a list */
List *insert_list_transition( List *l, Transition *tr) {
List *t = calloc(1,sizeof(List));
List *head = l;
while(l->next!=NULL)
l = l->next;
t->content = tr;
t->next = NULL;
l->next = t;
return head;
}
void print_tape( Tape *t,char blank) {
char c;
while(1) {
if(t->content != blank) break;
t= t->right;
}
while(1) {
if(t==NULL) break;
c = t->content;
if(t->content != blank)
putchar(c);
t= t->right;
}
putchar('\n');
}
void print_transition (Transition *t) {
char s1[] = "Left";
char s2[] = "Right";
if(t==NULL) {
printf("NULL Transfer");
return;
}
printf("current:%c tape:%c new state:%c new tape:%c direction %s\n",t->current_state,t->tape_symbol,t->new_state,t->new_tape_symbol,(t->dir == LEFT)?s1:s2);
}
/*test if the char c is in the string s */
int contains ( char c, char *s ) {
int i=0;
while(1) {
if(c== s[i]) return 1;
if(s[i] == '\0') return 0;
i++;
}
}
/* test if the input is a valid input */
int is_valid_input( char *input_alpha, char *input ) {
int i=0;
char c;
while(1) {
c = input[i];
if(c == '\0') break;
if(!contains(c,input_alpha)) return 0;
i++;
}
return 1;
}
TM *createTM (char *input) {
TM *m = calloc(1,sizeof(TM));
List *tr = calloc(1,sizeof(List));
char *buffer;
/*read input alphabet of PDA*/
buffer = strtok(input,":");
if(buffer == NULL) {
printf("Error in reading input alphabet!\n");
exit(1);
}
m->input_alpha = buffer;
/*read tape alphabet*/
buffer = strtok(NULL,":");
if(buffer == NULL) {
printf("Error in reading tape alphabet!\n");
exit(1);
}
m->tape_alpha = buffer;
/*read input sequence*/
buffer = strtok(NULL,":");
if(buffer == NULL) {
printf("Error in reading input sequence!\n");
exit(1);
}
if(!is_valid_input(m->input_alpha,buffer)) {
printf("Error! Input contains some invalid characters that don't match the input alphabet!\n");
exit(1);
}
m->input = buffer;
buffer = strtok(NULL,":");
m->start = buffer[0];
buffer = strtok(NULL,":");
m->accept = buffer[0];
buffer = strtok(NULL,":");
m->reject = buffer[0];
/*read tape transition*/
while(1) {
buffer = strtok(NULL,":");
if(buffer == NULL) break;
tr = insert_list(tr,buffer);
}
m->transition = tr->next;
return m;
}
Transition *find_transition(List * list,char state, char tape_symbol) {
Transition *t;
while(1) {
if(list==NULL) return NULL;
t = list -> content;
if(t->current_state == state && t->tape_symbol == tape_symbol)
return t;
list = list->next;
}
}
Tape *move(Tape *t,Direction dir, char blank) {
if(dir == LEFT) {
if(t->left==NULL) {
t = insert_tape(t,LEFT,blank);
}
return t->left;
}
if(dir == RIGHT) {
if(t->right==NULL) {
t = insert_tape(t,RIGHT,blank);
}
return t->right;
}
return NULL;
}
void simulate( TM *m ) {
/* first symbol in input symbol used to represent the blank symbol */
const char blank = m->tape_alpha[0];
char current_state = m->start;
Tape *tape = create_tape(m->input);
Tape *current_tape = tape;
char current_tape_symbol;
Transition *current_transition;
while(1) {
if(current_state == m->accept) {
printf("Accept\n");
print_tape(tape,blank);
break;
}
if(current_state == m->reject) {
printf("Reject\n");
print_tape(tape,blank);
break;
}
current_tape_symbol = (current_tape==NULL||current_tape ->content == '\0')?blank:current_tape->content;
current_transition = find_transition(m->transition,current_state,current_tape_symbol);
current_state = current_transition -> new_state;
current_tape -> content = current_transition -> new_tape_symbol;
current_tape = move( current_tape, current_transition ->dir, blank);
}
}
int main(void) {
char s[300];
TM *p;
scanf("%s",s);
p = createTM(s);
simulate(p);
return 0;
}
【问题讨论】：
-
为什么是 c++ 标签？
-
刚刚解决了这个问题，并简化了问题
-
在维基百科中查找图灵机的正式定义。
-
图灵机和下推自动机不是一回事。该代码并未将自己标记为图灵机的实现。
-
输入的描述不完整，没有说明
:a:ad:这两个字段既不是输入字母也不是堆栈字母，也不是输入不是转换（长度为5的字段- - 对应于Transition结构中的 5 个字符）。我的猜测是a是开始状态，ad是接受状态。查看代码的作用，并将其与维基百科中 PDA 的正式定义进行比较。
标签： c turing-machines