题意：训练指南P244

分析：链表模拟，维护链表的head和tail指针

#include 
     
      using namespace std;const int N = 1e5 + 5;struct Link_list    {    char ch;    Link_list *nex;}link_list[N];int main(void)  {    while (true) {         Link_list *head = link_list;         Link_list *q = link_list + 1;         head -> nex = NULL;         Link_list *tail = head, *pos = head;         char c;         while (true)  {            c = getchar ();            if (c == '\n')  break;            if (c == EOF)   return 0;            if (c != '[' && c != ']') {                Link_list *p = q++;                p -> ch = c;                p -> nex = pos -> nex;                pos -> nex = p;                pos = p;                if (tail -> nex != NULL)    tail = pos;            }            else if (c == '[')  pos = head;            else    pos = tail;         }         Link_list *p = head -> nex;         while (p)   {             printf ("%c", p -> ch);             p = p -> nex;         }         puts ("");    }    return 0;}