Prime Path

http://poj.org/problem?id=3126

 1 #include<cstdio>

 2 #include<iostream>

 3 #include<cstring>

 4 using namespace std;

 5 

 6 struct node

 7 {

 8     int k,step;

 9 };

10 

11 node h[100000];

12 bool p[11000];

13 int x,y,tot,s[11000];

14 

15 void make(int n)

16 {

17     memset(p,0,sizeof(p));

18     p[0]=1;

19     p[1]=1;

20     for(int i=2; i<=n; i++) if(!p[i])

21             for(int j=i*i; j<=n; j+=i) p[j]=1;

22 }

23 

24 int change(int x,int i,int j)

25 {

26     if(i==1) return (x/10)*10+j;else

27     if(i==2) return (x/100)*100+x%10+j*10;else

28     if(i==3) return (x/1000)*1000+x%100+j*100;else

29     if(i==4) return (x%1000)+j*1000;

30 }

31 

32 int main()

33 {

34     make(9999);

35     cin>>tot;

36     while(tot--)

37     {

38         cin>>x>>y;

39         h[1].k=x;

40         h[1].step=0;

41         int l=1,r=1;

42         memset(s,100,sizeof(s));

43         int ans=-1;

44         while(1)

45         {

46             if(h[l].k==y)

47             {

48                 ans=h[l].step;

49                 break;

50             }

51             int tk,ts;

52             for(int i=1; i<=4; i++)

53             {

54                 for(int j=0; j<=9; j++)

55                 {

56                     if(!((j==0)&&(i==4)))

57                     {

58                         tk=change(h[l].k,i,j);

59                         if(p[tk]) continue;

60                         ts=h[l].step+1;

61                         if(ts>=s[tk]) continue;

62                         if(tk==y)

63                         {

64                             ans=ts;

65                             break;

66                         }

67                         s[tk]=ts;

68                         r++;

69                         h[r].k=tk;

70                         h[r].step=ts;

71                     }

72                 }

73 

74             }

75             if(l==r||ans>=0) break;

76             l++;

77 

78         }

79         if(ans>=0) cout<<ans<<endl;

80         else cout<<" Impossible"<<endl;

81 

82     }

83     return 0;

84 }

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