86 lines
1.9 KiB
C++
86 lines
1.9 KiB
C++
#include<cstdio>
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#include<cstring>
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#include<queue>
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#include<algorithm>
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using namespace std;
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struct DT { int x,y,lie; };
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char s[505][505];
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DT st,ed;
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int n,m,d[505][505][3];
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queue<DT> Q;
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const int dx[4]={0,0,-1,1},dy[4]={-1,1,0,0};
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inline bool valid(int x,int y) { return x>=1&&y>=1&&x<=n&&y<=m; }
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void init()
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{
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for(int i=1;i<=n;i++) for(int j=1;j<=m;j++)
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if(s[i][j]=='O') { ed.x=i; ed.y=j; ed.lie=0; s[i][j]='.'; }
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else if(s[i][j]=='X')
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{
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for(int k=0;k<4;k++)
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{
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int x=i+dx[k],y=j+dy[k];
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if(valid(x,y)&&s[x][y]&&s[x][y]=='X')
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{
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st.x=min(i,x),st.y=min(j,y);
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st.lie=k<2?1:2;
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s[i][j]=s[x][y]='.';
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break;
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}
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}
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if(s[i][j]=='X') st.x=i,st.y=j,st.lie=0;
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}
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}
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inline bool valid(DT nxt)
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{
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if(!valid(nxt.x,nxt.y)) return 0;
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if(s[nxt.x][nxt.y]=='#') return 0;
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if(nxt.lie==0&&s[nxt.x][nxt.y]!='.') return 0;
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if(nxt.lie==1&&s[nxt.x][nxt.y+1]=='#') return 0;
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if(nxt.lie==2&&s[nxt.x+1][nxt.y]=='#') return 0;
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return 1;
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}
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const int nxt_x[3][4]={{0,0,-2,1},{0,0,-1,1},{0,0,-1,2}};
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const int nxt_y[3][4]={{-2,1,0,0},{-1,2,0,0},{-1,1,0,0}};
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const int nxt_lie[3][4]={{1,1,2,2},{0,0,1,1},{2,2,0,0}};
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int bfs()
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{
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for(int i=1;i<=n;i++) for(int j=1;j<=m;j++) for(int k=0;k<3;k++) d[i][j][k]=-1;
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while(Q.size()) Q.pop();
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d[st.x][st.y][st.lie]=0; Q.push(st);
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while(Q.size())
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{
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DT u=Q.front(); Q.pop();
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for(int i=0;i<4;i++)
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{
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DT nxt;
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nxt.x=u.x+nxt_x[u.lie][i];
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nxt.y=u.y+nxt_y[u.lie][i];
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nxt.lie=nxt_lie[u.lie][i];
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if(!valid(nxt)) continue;
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if(d[nxt.x][nxt.y][nxt.lie]==-1)
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{
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d[nxt.x][nxt.y][nxt.lie]=d[u.x][u.y][u.lie]+1;
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Q.push(nxt);
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if(nxt.x==ed.x&&nxt.y==ed.y&&nxt.lie==ed.lie) return d[nxt.x][nxt.y][nxt.lie];
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}
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}
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}
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return -1;
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}
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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while(scanf("%d%d",&n,&m)==2&&n)
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{
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for(int i=1;i<=n;i++) scanf("%s",s[i]+1);
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init();
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int res=bfs();
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if(res==-1) puts("Impossible");
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else printf("%d\n",res);
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}
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return 0;
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}
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