E

http://codeforces.com/contest/1023/problem/E

交互题

 #include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <time.h>
#include <string>
#include <set>
#include <map>
#include <list>
#include <stack>
#include <queue>
#include <vector>
#include <bitset>
#include <ext/rope>
#include <algorithm>
#include <iostream>
using namespace std;
#define ll long long
#define minv 1e-6
#define inf 1e9
#define pi 3.1415926536
#define E  2.7182818284
const ll mod=1e9+7;//998244353
const int maxn=1e5+10;

char S[10];
int s[1000],t[1000];

int main()
{
    int n,x,y,tot,xx,yy,i;
    scanf("%d",&n);
    x=n,y=n,tot=2*n;
    while (x-1+y-1>=n)
    {
        tot--;
        s[tot]=x;
        t[tot]=y;

        printf("? %d %d %d %d
",1,1,x-1,y);
        fflush(stdout);
        scanf("%s",S);
        if (strcmp(S,"YES")==0)
            x--;
        else
            y--;
    }
    tot--;
    s[tot]=x;
    t[tot]=y;

    xx=x,yy=y;

    tot=0;
    x=1,y=1;
    while (x!=xx || y!=yy)
    {
        tot++;
        s[tot]=x;
        t[tot]=y;

        printf("? %d %d %d %d
",x,y+1,n,n);
        fflush(stdout);
        scanf("%s",S);
        if (strcmp(S,"YES")==0)
            y++;
        else
            x++;
    }

    printf("! ");
    for (i=2;i<=2*n-1;i++)
        if (s[i]==s[i-1])
            printf("R");
        else
            printf("D");
    return 0;
}