Codeforces1023E Down or Right 【贪心】

题目分析:

从起点开始询问终点连通性，优先右走。从终点开始询问起点连通性，优先上走。

代码：

#include<bits/stdc++.h>
using namespace std;

int n;

int query(int x1,int y1,int x2,int y2){
    printf("? %d %d %d %d
",x1,y1,x2,y2);
    fflush(stdout);
    char str[5];
    scanf("%s",str);
    if(str[0] == 'Y') return 1;
    else return 0;
    //int z; scanf("%d",&z);
    //return z;
}

stack<char> sta;
vector <char> vc;
void work(){
    int x = 1,y = 1;
    while(n-x+n-y > n-1){
    int z = query(x,y+1,n,n);
    if(z){vc.push_back('R');y++;}
    else{vc.push_back('D');x++;}
    }
    int nx = n,ny = n;
    while(nx != x || ny != y){
    int z = query(1,1,nx-1,ny);
    if(z){sta.push('D');nx--;}
    else{sta.push('R');ny--;}
    }
    printf("! ");
    for(int i=0;i<vc.size();i++) printf("%c",vc[i]);
    while(!sta.empty()){printf("%c",sta.top());sta.pop();}
}

int main(){
    scanf("%d",&n);
    work();
    return 0;
}