CodeForces 670E Correct Bracket Sequence Editor

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<iostream>
using namespace std;
typedef long long LL;
const double pi=acos(-1.0),eps=1e-6;
void File()
{
    freopen("D:\\in.txt","r",stdin);
    freopen("D:\\out.txt","w",stdout);
}
template <class T>
inline void read(T &x)
{
    char c=getchar(); x=0;
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) {x=x*10+c-‘0‘; c=getchar();}
}

const int maxn=500010;
struct X
{
    bool f;
    int nx,pr;
}s[maxn];

char t[maxn],op[maxn];
int n,m,p;
stack<int>S;
int flag[maxn];
int f1[maxn],f2[maxn];

int main()
{
    scanf("%d%d%d",&n,&m,&p); p--;
    scanf("%s",t); int len=strlen(t);

    for(int i=0;t[i];i++)
    {
        if(S.empty()) S.push(i);
        else
        {
            if(t[i]==‘(‘) S.push(i);
            else
            {
                if(t[S.top()]==‘(‘)
                {
                    f1[S.top()]=i, f2[i]=S.top();
                    S.pop();
                }
                else S.push(i);
            }
        }
    }

    for(int i=0;i<len;i++)
    {
        if(t[i]==‘(‘) s[i].f=0; else s[i].f=1;
        s[i].pr=s[i].nx=-1;
        if(i!=0) s[i].pr=i-1; if(i!=len-1) s[i].nx=i+1;
    }

    scanf("%s",op);
    for(int i=0;op[i];i++)
    {
        if(op[i]==‘L‘) p=s[p].pr;
        else if(op[i]==‘R‘) p=s[p].nx;
        else
        {
            int pos1=p,pos2;
            if(s[p].f==0) pos2=f1[p]; else pos2=f2[p];
            if(pos1>pos2) swap(pos1,pos2);

           // for(int j=pos1;j<=pos2;j++) flag[j]=1;
            flag[pos1]++;
            flag[pos2+1]--;

            if(s[pos1].pr!=-1) s[s[pos1].pr].nx=s[pos2].nx;
            if(s[pos2].nx!=-1) s[s[pos2].nx].pr=s[pos1].pr;

            if(s[pos2].nx!=-1) p=s[pos2].nx;
            else p=s[pos1].pr;

        }
    }

    LL sum=0;

  //  for(int i=0;i<len;i++) printf("%d ",flag[i]);
   // printf("\n");
    for(int i=0;i<len;i++)
    {
        sum=sum+flag[i];
        if(sum>0) continue;
        printf("%c",t[i]);
    }
    printf("\n");
    return 0;
}