题意：
n<=500
思路：From https://blog.csdn.net/csdnjiangshan/article/details/81813227
1 #include<cstdio> 2 #include<cstring> 3 #include<string> 4 #include<cmath> 5 #include<iostream> 6 #include<algorithm> 7 #include<map> 8 #include<set> 9 #include<queue> 10 #include<vector> 11 #include<bitset> 12 using namespace std; 13 typedef long long ll; 14 typedef unsigned int uint; 15 typedef unsigned long long ull; 16 typedef pair<int,int> PII; 17 typedef vector<int> VI; 18 #define fi first 19 #define se second 20 #define MP make_pair 21 #define N 210000 22 #define M 51 23 #define MOD 1000000007 24 #define eps 1e-8 25 #define pi acos(-1) 26 #define oo 1e9 27 28 char s[10]; 29 int ans[N]; 30 31 int query(int x1,int y1,int x2,int y2) 32 { 33 printf("? %d %d %d %d ",x1,y1,x2,y2); 34 fflush(stdout); 35 scanf("%s",s); 36 if(s[0]=='Y') return 1; 37 return 0; 38 } 39 40 int calc(int x1,int y1,int x2,int y2) 41 { 42 return abs(x1-x2)+abs(y1-y2); 43 } 44 45 int main() 46 { 47 int n; 48 scanf("%d",&n); 49 int x=1,y=1; 50 int k=0; 51 while(calc(x,y,n,n)>=n) 52 { 53 if(y+1<=n&&query(x,y+1,n,n)) 54 { 55 y++; ans[++k]='R'; 56 } 57 else 58 { 59 x++; ans[++k]='D'; 60 } 61 } 62 k=2*n-1; x=n; y=n; 63 while(calc(x,y,1,1)>=n) 64 { 65 if(x-1>0&&query(1,1,x-1,y)) 66 { 67 x--; ans[--k]='D'; 68 } 69 else 70 { 71 y--; ans[--k]='R'; 72 } 73 } 74 printf("! "); 75 for(int i=1;i<=2*n-2;i++) printf("%c",ans[i]); 76 return 0; 77 }