题目链接
Sample Input
This_is_a_[Beiju]_text
[[]][][]Happy_Birthday_to_Tsinghua_University

Sample Output
BeijuThis_is_a__text
Happy_Birthday_to_Tsinghua_University

一开始不用指针实现链表，但是写的时候发现这题用数组实现链表会很麻烦，写不来，于是重新用指针写链表，然而写出来后提交上去显示时间超限T-T…

链表实现的代码：

#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
using namespace std;
int flag;
typedef struct lt* Next;
struct lt
{
	char c;
	Next next;
	lt():next(NULL){}
};
Next head = NULL;

void Free() {
	Next t = head->next, t2 = t->next;
	while (t != NULL) {
		t2 = t->next;
		free(t);
		t = t2;
	}
	free(head);
}

int main()
{
	Next h2;
	string letter;
	while (cin >> letter) {
		flag = 0;
		head = new struct lt();
		h2 = head;
		for (int i = 0; i < letter.length(); i++) {
			if (letter[i] != '[' && letter[i] != ']') {
				if (flag) {
					Next h = new struct lt();
					h->c = letter[i];
					h2 = h;
					i += 1;
					while (letter[i] != ']') {
						Next tmp = new struct lt();
						tmp->c = letter[i];
						h2->next = tmp;
						h2 = tmp;
						i++;
					}
					h2->next = head->next;
					head->next = h;
					i -= 1;
				}
				else {
					Next n = new struct lt();
					n->c = letter[i];
					h2->next = n;
					h2 = n;
				}
			}
			else if (letter[i] == '[') {
				flag = 1;
			}
			else if (letter[i] == ']') {
				flag = 0;
				h2 = head->next;
				if (h2 == NULL) {
					h2 = head;
				}
				else {
					while (h2->next != NULL) {
						h2 = h2->next;
					}
				}
			}
		}
		h2 = head->next;
		while (h2 != NULL) {
			cout << h2->c;
			h2 = h2->next;
		}
		Free();
		putchar('\n');
	}
	return 0;
}

重新看一遍自己的代码，觉得可能是释放内存那占了时间，但是去掉Free()函数依然超时

书上的代码：

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
const int maxn = 100100;
int Next[maxn], cur, last;
char s[maxn];

int main() {
	//freopen("D://in.txt", "r", stdin);
	while (scanf("%s", s + 1) == 1) { // 从数组的第一位开始读数据
		cur = last = 0;
		int len = strlen(s + 1);
		Next[0] = 0; // 链表初始化
		for (int i = 1; i <= len; i++) {
			if (s[i] == '[') {
				cur = 0; // 返回到表头
			}
			else if (s[i] == ']') {
				cur = last;
			}
			else {
				Next[i] = Next[cur]; // attention
				Next[cur] = i;
				if (cur == last) {
					last = i;
				}
				cur = i;
			}
		}
		for (int i = Next[0]; i != 0; i = Next[i]) {
			cout << s[i];
		}
		putchar('\n');
	}
}

attention：看了好一会儿才明白这行代码什么意思，这行代码的意思是让链表的末尾元素始终指向next[0],如果没有检查文本的过程中没有碰到’ [ ',则链表末尾的元素一直指向next[0]（也就是 0 ），如果碰到’ [ ', 则 [xxx] ,xxx内的元素会一直指向next[0], 也就是真正的表头，比如题目的数据为 [Beiju]

后面的依此类推