hdu 4770 Lights Against Dudely

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题目:http://acm.hdu.edu.cn/showproblem.php?pid=4770

因为最多只能放15盏灯,所以我们可以枚举在哪些位置放灯,又因为只有一盏灯可以旋转,所以我们可以在前面的基础上枚举旋转哪盏灯,并且枚举旋转方向.

答案最理想的情况是0,所以我们可以从0开始,不可行的话,就把答案+1;

#include<stdio.h>#include<string.h>#include<algorithm>#include<map>#include<vector>using namespace std;#define rep(i,s,t) for(int i=s;i<t;i++)typedef pair<int,int>ii;int n,m,Size,len;char s[210][210];map<ii,bool>vis;vector<int>v[16],choose;vector<ii>node;int dx[]={-1,-1,1,1};int dy[]={-1,1,-1,1};inline int getone(int i){int ret=0;while(i) {ret++,i-=i&(-i);}return ret;}inline void Init(){int all=(1<<Size);rep(i,1,all){v[getone(i)].push_back(i);}}inline bool ok(int x,int y,int xx,int yy){if(xx>=0 && xx<n){if(s[xx][y]=='#') return 0;}if(yy>=0 && yy<m){if(s[x][yy]=='#') return 0;}return 1;}inline bool flood(int now){rep(i,0,len){if(i!=now){int x=node[choose[i]].first,y=node[choose[i]].second;int xx=x-1,yy=y+1;if(!ok(x,y,xx,yy)) return 0;vis[node[choose[i]]]=vis[ii(x,yy)]=vis[ii(xx,y)]=1;}}return 1;}inline bool check(int now,int j){int x=node[choose[now]].first,y=node[choose[now]].second;vis.clear();int xx=x+dx[j],yy=y+dy[j];if(!ok(x,y,xx,yy)) return 0;if(!flood(now)) return 0;vis[ii(x,yy)]=vis[ii(xx,y)]=vis[node[choose[now]]]=1;rep(i,0,Size){if(!vis[node[i]]) return 0;}return 1;}inline bool dfs(int tmp){int S=v[tmp].size();rep(i,0,S){int st=v[tmp][i];choose.clear();rep(j,0,Size){if(st&(1<<j)) choose.push_back(j);}len=choose.size();rep(j,0,len){if(check(j,0)) return 1;if(check(j,1)) return 1;if(check(j,2)) return 1;if(check(j,3)) return 1;}}return 0;}int main(){while(scanf("%d%d",&n,&m), n||m){node.clear();rep(i,0,n){scanf("%s",s[i]);rep(j,0,m){if(s[i][j]=='.'){node.push_back(ii(i,j));}}}Size=node.size();if(Size==0){puts("0");continue;}rep(i,1,Size+1) v[i].clear();Init();int ans=1;while(ans<=Size && !dfs(ans)) ans++;if(ans==Size+1) puts("-1");else printf("%d\n",ans);}return 0;}

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