双指针过不了样例求调qaq

#include<bits/stdc++.h>
using namespace std;
const int N = 2e6 + 5;
int n;
int t,a[N];
deque<char> qwq;
int l = 1,r = 2 * n;//当前选择 
int L,R;
int main(){
	cin >> t;
	while(t--){
		cin >> n;
		l = 1;r = 2 * n; 
		cin >> a[1];
		int ans = a[1];
		for(int i = 2;i <= 2 * n;i++){
			cin >> a[i];
			ans ^= a[i];
			if(a[i] == a[1]){
				L = i + 1;
				R = i - 1;
			}
		}
		if(ans != 0){
			cout<<-1<<endl;
			continue;
		}
		bool f = 1;
		for(int i = 1;i <= n;i++){//n次选择 
			if(l < L){//选择开头
				if(a[l] == a[L - 1]&&l < L - 1){
					qwq.push_back('L');
					L--;
					l++;
				}else if(a[l] == a[R + 1]&&R + 1 < r){
					qwq.push_back('L');
					R++;
					l++;
				}
			}else if(r > R){//选择结尾
				if(a[r] == a[L - 1]&&l < L - 1){
					qwq.push_back('R');
					L--;
					r--;
				}else if(a[r] == a[R + 1]&&R + 1 < r){
					qwq.push_back('R');
					R++;
					r--;
				}
			}else{//输出-1 
				f = 0;
			}

		}
		if(f){
			while(!qwq.empty()){
				cout<<qwq.front();
				qwq.pop_front();
			}
		}else{
			cout<<-1;
		}
		cout<<endl;		
	}
	return 0;
}