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brackets_on_stack.c
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brackets_on_stack.c
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/* Check if the brackets sequence
is correct or not via
doubly linked list data structure
[, {, <, (, ), >, }, ] are only possible brackets
Sources:
http://e-maxx.ru/algo/bracket_sequences [ru]
Example:
{<>} -> YES
[{<}>] -> NO
*/
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
struct Node
{
char Data;
struct Node* next;
struct Node* back;
};
struct List
{
struct Node* head;
};
struct List* list_new()
{
/*
* initialize new list
*/
struct List* list;
list = (struct List *) malloc(sizeof(struct List));
if (list == NULL)
{
fprintf(stderr, "Can't allocate memory %s\n", strerror(errno));
fprintf(stderr, "Error in function list_new()\n");
return NULL;
}
list->head = NULL;
return list;
}
int check_empty(struct List* list)
{
if (list->head == NULL)
{
return 1;
}
return 0;
}
void push(struct List* list, char a)
{
/*
* add element a to the end of the list
*/
if (check_empty(list) == 1)
{
struct Node* node;
node = (struct Node *)malloc(sizeof(struct Node));
node->Data = a;
node->back = NULL;
node->next = NULL;
list->head = node;
return;
}
struct Node* node;
node = (struct Node *)malloc(sizeof(struct Node));
if (node == NULL)
{
fprintf(stderr, "Can't allocate memory: %s\n", strerror(errno));
fprintf(stderr, "Error in function push with arguement %d\n", a);
return;
}
node->Data = a;
node->next = NULL;
node->back = list->head;
list->head = node;
}
void unshift(struct List *list, char a)
{
/*
* add element a to the begining of the list
*/
struct Node* node_pointer;
node_pointer = list->head;
if (node_pointer == NULL)
{
push(list, a);
return;
}
while (node_pointer->back != NULL)
{
node_pointer = node_pointer->back;
}
struct Node* Node;
Node = (struct Node *)malloc(sizeof(struct Node));
if (Node == NULL)
{
fprintf(stderr, "Can't allocate memory: %s\n", strerror(errno));
fprintf(stderr, "Error in function unshift with arguement %d\n", a);
return;
}
Node->Data = a;
Node->back = NULL;
Node->next = node_pointer;
node_pointer->back = Node;
}
void pop(struct List *list, char *x)
{
/*
* take the last element from list
* and place it in x variable
*/
if (check_empty(list) == 1)
{
return;
}
*x = list->head->Data;
struct Node* node = list->head;
list->head = list->head->back;
free(node);
if (check_empty(list) == 0)
{
list->head->next = NULL;
return;
}
list->head = NULL;
}
void shift(struct List *list, char *x)
{
/*
* take the first element from list
* and place it in x variable
*/
if (check_empty(list) == 1)
{
return;
}
struct Node* node_pointer = list->head;
if (node_pointer->back == NULL)
{
*x = node_pointer->Data;
free(node_pointer);
list->head = NULL;
return;
}
while (node_pointer->back != NULL)
{
node_pointer = node_pointer->back;
}
*x = node_pointer->Data;
node_pointer->next->back = NULL;
free(node_pointer);
return;
}
void list_reverse(struct List* list)
{
/*
* inverting list from [a,b,c,d] to [d,c,b,a]
*/
struct List* list_revers;
list_revers = list_new();
struct Node* node;
if (check_empty(list) == 1)
{
return;
}
node = list->head;
while (node != NULL)
{
push(list_revers, node->Data);
struct Node *free_node = node;
node = node->back;
free(free_node);
}
*list = *list_revers;
}
void print(struct List* list)
{
struct Node* node = list->head;
while (node != NULL)
{
printf("%c ", node->Data);
node = node->back;
}
printf("\n");
}
int main()
{
struct List* list;
list = list_new();
char s = 1;
while (s != '\n')
{
scanf("%c", &s);
if (s=='(' || s=='<' || s=='{' || s=='[')
push(list, s);
if (s==')')
{
char x;
pop(list, &x);
if (x!='(')
break;
}
if (s=='}')
{
char x;
pop(list, &x);
if (x!='{')
break;
}
if (s=='>')
{
char x;
pop(list, &x);
if (x!='<')
break;
}
if (s==']')
{
char x;
pop(list, &x);
if (x!='[')
break;
}
}
if (check_empty(list) == 1)
printf("YES\n");
else
printf("NO\n");
return 0;
}