111 lines
2.5 KiB
C++
111 lines
2.5 KiB
C++
#include<iostream>
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#include<cstring>
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#include<cstdio>
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#include<queue>
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#define N 40400
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#define MAX 210
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#define CNT 4000
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using namespace std;
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bool isprime[N];
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int prime[CNT],cnt;
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int map[MAX][MAX];
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bool visited[MAX][MAX];
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struct point{int x,y,step;};
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void find_prime()
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{
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int i,j;
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cnt=0;
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memset(isprime,true,sizeof(isprime));
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isprime[1]=false;
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for(i=2;i<N;i++)
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{
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if(isprime[i])
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{
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prime[cnt++]=i;
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for(j=2*i;j<N;j=j+i) isprime[j]=false;
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}
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}
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}
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void build_map(int p,int q,int s,int c)
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{
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if(s==0) return ;
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int i;
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for(i=q;i<q+c;i++) map[p][i]=s--;
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for(i=p+1;i<p+c;i++) map[i][q+c-1]=s--;
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for(i=q+c-2;i>q;i--) map[p+c-1][i]=s--;
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for(i=p+c-1;i>p;i--) map[i][q]=s--;
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build_map(p+1,q+1,s,c-2);
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}
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int t_i,t_j;
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void find(int u)
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{
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int i,j;
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for(i=1;i<=200;i++)
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{
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for(j=1;j<=200;j++)
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{
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if(u==map[i][j])
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{
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t_i=i;t_j=j;
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return ;
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}
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}
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}
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}
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int BFS(int u,int v)
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{
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find(u);
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point t,tt;
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t.x=t_i;t.y=t_j;t.step=0;
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queue<point>Q;
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while(!Q.empty()) Q.pop();
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Q.push(t);
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visited[t.x][t.y]=true;
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while(!Q.empty())
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{
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t=Q.front();Q.pop();
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if(map[t.x][t.y]==v) return t.step;
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if(t.x-1>=1&&!visited[t.x-1][t.y]&&!isprime[map[t.x-1][t.y]])
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{
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tt.x=t.x-1;tt.y=t.y;tt.step=t.step+1;
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Q.push(tt);
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visited[tt.x][tt.y]=true;
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}
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if(t.x+1<=200&&!visited[t.x+1][t.y]&&!isprime[map[t.x+1][t.y]])
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{
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tt.x=t.x+1;tt.y=t.y;tt.step=t.step+1;
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Q.push(tt);
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visited[tt.x][tt.y]=true;
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}
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if(t.y-1>=1&&!visited[t.x][t.y-1]&&!isprime[map[t.x][t.y-1]])
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{
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tt.x=t.x;tt.y=t.y-1;tt.step=t.step+1;
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Q.push(tt);
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visited[tt.x][tt.y]=true;
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}
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if(t.y+1<=200&&!visited[t.x][t.y+1]&&!isprime[map[t.x][t.y+1]])
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{
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tt.x=t.x;tt.y=t.y+1;tt.step=t.step+1;
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Q.push(tt);
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visited[tt.x][tt.y]=true;
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}
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}
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return 0;
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}
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int main()
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{
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int u,v,k=1;
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memset(map,0,sizeof(map));
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find_prime();
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build_map(1,1,40000,200);
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while(scanf("%d%d",&u,&v)!=EOF)
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{
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memset(visited,false,sizeof(visited));
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int ans;
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ans=BFS(u,v);
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if(ans) printf("Case %d: %d\n",k++,ans);
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else printf("Case %d: impossible\n",k++);
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}
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return 0;
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}
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