RT，求大佬帮忙看一下。

#include<bits/stdc++.h>
using namespace std;
long long n, arr[1000010], t;
struct node{
	string s;
}ans[1000010];
bool cmt(node x, node y){
	return x.s < y.s;
}
string solve1(long long x){
	long long l1 = 1, r1 = 2 * n + 1, l2 = x, r2 = x;
	string str1 = "L", str2 = "L";
	for(int i = 1; i < n; i++){
		if(arr[l1 + 1] == arr[l2 - 1] && l1 + 1 != l2 - 1){
			str1 = str1 + "L";
			str2 = "L" + str2;
			l1++;
			l2--;
//			cout << 1;
		}
		else if(arr[l1 + 1] == arr[r2 + 1] && l1 + 1 != l2 && r2 + 1 != r1){
			str1 = str1 + "L";
			str2 = "R" + str2;
			l1++;
			r2++;
//			cout << 2;
		}
		else if(arr[r1 - 1] == arr[l2 - 1] && r1 - 1 != r2 && l2 - 1 != r1){
			str1 = str1 + "R";
			str2 = "L" + str2;
			r1--;
			l2--;
//			cout << 3;
		}
		else if(arr[r1 - 1] == arr[r2 + 1] && r2 + 1 != r1 - 1){
			str1 = str1 + "R";
			str2 = "R" + str2;
			r1--;
			r2++;
//			cout << 4;
		}
		else return "";
	}
	return str1 + str2;
}
string solve2(long long x){
	long long l1 = 2, r1 = 2 * n, l2 = x, r2 = x;
	string str1 = "R", str2 = "L";
	for(int i = 1; i < n; i++){
		if(arr[l1 + 1] == arr[l2 - 1] && l1 + 1 != l2 - 1){
			str1 = str1 + "L";
			str2 = "L" + str2;
			l1++;
			l2--;
		}
		else if(arr[l1 + 1] == arr[r2 + 1] && l1 + 1 != l2 && r2 + 1 != r1){
			str1 = str1 + "L";
			str2 = "R" + str2;
			l1++;
			r2++;
		}
		else if(arr[r1 - 1] == arr[l2 - 1] && r1 - 1 != r2 && l2 - 1 != r1){
			str1 = str1 + "R";
			str2 = "L" + str2;
			r1--;
			l2--;
		}
		else if(arr[r1 - 1] == arr[r2 + 1] && r2 + 1 != r1 - 1){
			str1 = str1 + "R";
			str2 = "R" + str2;
			r1--;
			r2++;
		}
		else return "";
	}
}
int main(){
//	freopen("palin.in", "r", stdin);
//	freopen("palin.out", "w", stdout);
	cin >> t;
	while(t--){
		scanf("%lld", &n);
		for(int i = 1; i <= 2 * n; i++){
			scanf("%lld", &arr[i]);
		}
		long long tot = 0;
		string tmp;
		for(int i = 2 * n; i >= 2; i--){
			if(arr[i] == arr[1])tmp = solve1(i);
			if(tmp != ""){
				ans[++tot].s = tmp;
			}
		}
		for(int i = 2 * n - 1; i >= 1; i--){
			if(arr[i] == arr[n * 2])tmp = solve2(i);
			if(tmp != ""){
				ans[++tot].s = tmp;
			}
		}
		if(tot){
			sort(ans + 1, ans + tot + 1, cmt);
			cout << ans[1].s<<'\n';
		}
		if(!tot){
			cout << -1 << '\n';
		}
	}
	return 0;
}
//2
//5 
//4 1 2 4 5 3 1 2 3 5
//3
//3 2 1 2 1 3
//1
//20
//5 20 6 12 13 18 9 17 2 7 7 18 1 11 10 15 4 6 17 19 14 10 14 13 1 16 8 3 12 8 19 20 4 16 5 3 9 2 15 11