E.cpp

# pragma GCC optimize ("O3")
# pragma GCC optimize ("Ofast")
# pragma GCC optimize ("unroll-loops")

#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>

#pragma warning(disable:4996)
#pragma comment(linker, "/STACK:336777216")

using namespace std;
//using namespace __gnu_pbds;

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef tuple<int, int, int> ti3;
typedef tuple<int, int, int, int> ti4;
typedef stack<int> si;
typedef queue<int> qi;
typedef priority_queue<int> pqi;
typedef pair<ll, ll> pll;
typedef vector<ll> vl;
typedef tuple<ll, ll, ll> tl3;
typedef tuple<ll, ll, ll, ll> tl4;
typedef stack<ll> sl;
typedef queue<ll> ql;
typedef priority_queue<ll> pql;
//typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>ordered_set;

const int dx[4] = { 1,-1,0,0 };
const int dy[4] = { 0,0,1,-1 };
const int ddx[8] = { 0,0,1,1,1,-1,-1,-1 }, ddy[8] = { 1,-1,1,0,-1,1,0,-1 };
const int INF = 0x3f7f7f7f;
const ll INF_LL = 0x3f7f7f7f7f7f7f7f;
ll POW(ll a, ll b, ll MMM) { ll ret = 1; for (; b; b >>= 1, a = (a*a) % MMM)if (b & 1)ret = (ret*a) % MMM; return ret; }
ll GCD(ll a, ll b) { return b ? GCD(b, a%b) : a; }
ll LCM(ll a, ll b) { if (a == 0 || b == 0)return a + b; return a / GCD(a, b) * b; }
ll INV(ll a, ll m) {
	ll m0 = m, y = 0, x = 1;
	if (m == 1)	return 0;
	while (a > 1) {
		ll q = a / m;
		ll t = m;
		m = a % m, a = t;
		t = y;
		y = x - q * y;
		x = t;
	}
	if (x < 0) x += m0;
	return x;
}
pll EXGCD(ll a, ll b) {
	if (b == 0) return { 1,0 };
	auto t = EXGCD(b, a%b);
	return { t.second,t.first - t.second*(a / b) };
}
bool OOB(ll x, ll y, ll N, ll M) { return 0 > x || x >= N || 0 > y || y >= M; }
#define X first
#define Y second
#define rep(i,a,b) for(int i = a; i < b; i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define sz(a) ((int)(a.size()))
#define sf1(a) cin >> a
#define sf2(a,b) cin >> a >> b
#define sf3(a,b,c) cin >> a >> b >> c
#define sf4(a,b,c,d) cin >> a >> b >> c >> d
#define sf5(a,b,c,d,e) cin >> a >> b >> c >> d >> e
#define sf6(a,b,c,d,e,f) cin >> a >> b >> c >> d >> e >> f
#define pf1(a) cout << (a) << ' '
#define pf2(a,b) cout << (a) << ' ' << (b) << ' '
#define pf3(a,b,c) cout << (a) << ' ' << (b) << ' '<< (c) << ' '
#define pf4(a,b,c,d) cout << (a) << ' ' << (b) << ' '<< (c) << ' '<< (d) << ' '
#define pf5(a,b,c,d,e) cout << (a) << ' ' << (b) << ' '<< (c) << ' '<< (d) << ' '<< (e) << ' '
#define pf6(a,b,c,d,e,f) cout << (a) << ' ' << (b) << ' '<< (c) << ' '<< (d) << ' '<< (e) << ' ' << (f) << ' '
#define pf0l() cout << '\n';
#define pf1l(a) cout << (a) << '\n'
#define pf2l(a,b) cout << (a) << ' ' << (b) << '\n'
#define pf3l(a,b,c) cout << (a) << ' ' << (b) << ' '<< (c) << '\n'
#define pf4l(a,b,c,d) cout << (a) << ' ' << (b) << ' '<< (c) << ' '<< (d) << '\n'
#define pf5l(a,b,c,d,e) cout << (a) << ' ' << (b) << ' '<< (c) << ' '<< (d) << ' '<< (e) << '\n'
#define pf6l(a,b,c,d,e,f) cout << (a) << ' ' << (b) << ' '<< (c) << ' '<< (d) << ' '<< (e) << ' ' << (f) << '\n'
#define pfvec(V) for(auto const &t : V) pf1(t)
#define pfvecl(V) for(auto const &t : V) pf1(t); pf0l()
int N;
void ask1(int x1, int y1) { // ask for (N,N)
	cout << "? " << x1 << ' ' << y1 << ' ' << N << ' ' << N << endl;
}
void ask2(int x1, int y1) { // ask for (1,1)
	cout << "? " << 1 << ' ' << 1 << ' ' << x1 << ' ' << y1 << endl;
}

string ans;
string ans2;
int curX = 1;
int curY = 1; // (1,1)에서 대각선까지 도달
int main(void) {
	ios::sync_with_stdio(false);
	cin.tie(0);
	sf1(N);
	while (curX + curY < N + 1) {
		ask1(curX, curY + 1); // 오른쪽으로 이동할 경우
		string recv;
		sf1(recv);
		if (recv == "YES") {
			curY++;
			ans += 'R';
		}
		else {
			curX++;
			ans += 'D';
		}
	}

	int xx = N;
	int yy = N;
	while (xx + yy > N + 1) {
		ask2(xx-1, yy); // 직전에 위로 이동할 경우
		string recv;
		sf1(recv);
		if (recv == "YES") {
			xx--;
			ans2 += 'D';
		}
		else {
			yy--;
			ans2 += 'R';
		}
	}
	reverse(all(ans2));
	cout << "! " << ans + ans2 << endl;
}