【CF1023E】Down or Right（交互，贪心）

题意：

n<=500

思路：From https://blog.csdn.net/csdnjiangshan/article/details/81813227

#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<iostream>
#include<algorithm>
#include<map>
#include<set>
#include<queue>
#include<vector>
#include<bitset>
using namespace std;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef pair<int,int> PII;
typedef vector<int> VI;
#define fi first
#define se second 
#define MP make_pair
#define N      210000
#define M      51
#define MOD 1000000007
#define eps 1e-8 
#define pi     acos(-1)
#define oo     1e9

char s[10];
int ans[N];

int query(int x1,int y1,int x2,int y2)
{
    printf("? %d %d %d %d
",x1,y1,x2,y2);
    fflush(stdout);
    scanf("%s",s);
    if(s[0]=='Y') return 1;
    return 0;
}

int calc(int x1,int y1,int x2,int y2)
{
    return abs(x1-x2)+abs(y1-y2);
}

int main()
{ 
    int n; 
    scanf("%d",&n);
    int x=1,y=1;
    int k=0;
    while(calc(x,y,n,n)>=n)
    {
        if(y+1<=n&&query(x,y+1,n,n))
        {
            y++; ans[++k]='R';
        }
         else
         {
             x++; ans[++k]='D';
         }
    }
    k=2*n-1; x=n; y=n;
    while(calc(x,y,1,1)>=n)
    {
        if(x-1>0&&query(1,1,x-1,y))
        {
            x--; ans[--k]='D';
        }
         else
         {
             y--; ans[--k]='R';
         }
    }    
    printf("! ");
    for(int i=1;i<=2*n-2;i++) printf("%c",ans[i]);
    return 0;
}