E - Down or Right Codeforces Round #504 (rated, Div. 1 + Div. 2, based on VK Cup 2018 Final)

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+;//
 const int maxn=1e5+;

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

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

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

     xx=x,yy=y;

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

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

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