@[Scarlet_Lightning](/user/83345)
```c++
#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<stack>
using namespace std;
struct node{
int id;
char bracket;
};
stack<node> stk;
char bracket;
int i;
int ansbegin=-999999;
int anslen=0;
int ansend=-999999;
int sanslen;
char str[1200001];
bool vis[1200001];
inline bool matching(node ca,node cb){
if(ca.bracket==')')return cb.bracket=='(';
if(ca.bracket==']')return cb.bracket=='[';
return false;
}
inline int __max(int a,int b){
return a>b?a:b;
}
inline void Find_LongestRegular(){
int ansid=0, len = strlen(str);
for(i=0;i<len;++i)
{
if(!vis[i]){
sanslen=0;
ansid=i+1;
}
else{
sanslen++;
if(sanslen>anslen){
ansbegin=ansid;
ansend=i;
anslen=sanslen;
}
}
}
}
int main()
{
int match=0, len;
scanf("%s",&str);
len = strlen(str);
for(i=0;i<len;++i)
{
bracket=str[i];
node b;
b.bracket=bracket;
b.id=i;
stk.push(b);
//stk.ergodic();
if(bracket==')'||bracket==']'){
if(stk.size()==1){
continue;
}
stk.pop();
node top=stk.top();
stk.push(b);
if(matching(b,top)){
match++;
stk.pop();
stk.pop();
vis[b.id]=true;
vis[top.id]=true;
}
}
}
Find_LongestRegular();
for(i=ansbegin;i<=ansend;++i)
{
putchar(str[i]);
}
return 0;
}
```
by 红黑树 @ 2021-09-11 16:03:11
https://www.luogu.com.cn/record/57827662
by 红黑树 @ 2021-09-11 16:03:31
$strlen$ 会花费大量时间，可以先算好
by 红黑树 @ 2021-09-11 16:05:38
@[红黑树](/user/413140) 这是2019年的帖子，现在此题早已通过了，不过还是要感谢大佬的解答
by Scarlet_Lightning @ 2021-09-17 19:07:27