AcWing 827 双链表 （模板）

#include
#include

using namespace std;

const int N = 1e5 + 10;

int e[N], l[N], r[N], idx;
int m;
int r1 = -1, l1 = -1;

void remove(int k){
	r[l[k]] = r[k];
	l[r[k]] = l[k];
	if(k == l1) l1 = r[k];
	if(k == r1) r1 = l[k];
}

void insertR(int k, int x){
	e[idx] = x;
	r[idx] = r[k];
	l[idx] = k;
	l[r[k]] = idx;
	r[k] = idx;
	if(r1 == -1) r1 = idx;
	else if(r[idx] == -1) r1 = idx; 
	idx ++ ;
}

void insertL(int k, int x){
	e[idx] = x;
	r[idx] = k;
	l[idx] = l[k];
	r[l[k]] = idx;
	l[k] = idx;
	if(l1 == -1) l1 = idx;
	else if(l[idx] == -1) l1 = idx;
	idx ++ ;
} 
int main()
{
	cin>>m;
	memset(r, -1, sizeof(r));
	memset(l, -1, sizeof(l));
	while(m -- ){
		string op;
		cin>>op;
		if(op == "L"){
			int x;
			cin>>x;
			if(idx == 0){
				e[idx] = x;
				l1 = idx;
				r1 = idx;
				idx ++ ;
			}
			else{
				e[idx] = x;
				r[idx] = l1;
				l[l1] = idx;
				l1 = idx;
				if(r1 == -1) r1 = idx;
				idx ++ ;
			}
		}
		else if(op == "R"){
			int x;
			cin>>x;
			if(idx == 0){
				e[idx] = x;
				l1 = idx;
				r1 = idx;
				idx ++ ;
			}
			else{
				e[idx] = x;
				l[idx] = r1;
				r[r1] = idx;
				r1 = idx;
				if(l1 == -1) l1 = idx;
				idx ++ ;
			}
		}
		else if(op == "D"){
			int k;
			cin>>k;
			if(k == 1 && idx == 1){
				l1 = -1;
				r1 = -1;
			}
			remove(k - 1);
		} 
		else if(op == "IR"){
			int k, x;
			cin>>k>>x;
			insertR(k - 1, x);
		}
		else if(op == "IL"){
			int k, x;
			cin>>k>>x;
			insertL(k - 1, x);
		}
	}
	for(int i = l1; i != -1; i = r[i]){
		cout<