poj3126

BFS，因为这题是4位数，所以要判断是不是素数只需要100以下的素数，先生成100以下素数表。

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      #include 
    
      <
    
      iostream
    
      >
    
      
#include 
    
      <
    
      cstdlib
    
      >
    
      
#include 
    
      <
    
      cstring
    
      >
    
      
#include 
    
      <
    
      cstdio
    
      >
    
      
#include 
    
      <
    
      queue
    
      >
    
      

    
      using
    
       
    
      namespace
    
       std;


    
      struct
    
       item
{
 
    
      int
    
       num[
    
      4
    
      ];
} a, b;


    
      int
    
       prime[
    
      100
    
      ], primenum, cost[
    
      10000
    
      ];


    
      int
    
       toint(item 
    
      &
    
      a)
{
 
    
      int
    
       ans 
    
      =
    
       
    
      0
    
      ;
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       
    
      4
    
      ; i
    
      ++
    
      )
 ans 
    
      =
    
       ans 
    
      *
    
       
    
      10
    
       
    
      +
    
       a.num[i];
 
    
      return
    
       ans;
}


    
      void
    
       makeprime()
{
 primenum 
    
      =
    
       
    
      1
    
      ;
 prime[
    
      0
    
      ] 
    
      =
    
       
    
      2
    
      ;
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      3
    
      ; i 
    
      <
    
       
    
      100
    
      ; i
    
      ++
    
      )
 {
 
    
      bool
    
       ok 
    
      =
    
       
    
      true
    
      ;
 
    
      for
    
       (
    
      int
    
       j 
    
      =
    
       
    
      0
    
      ; prime[j] 
    
      *
    
       prime[j] 
    
      <=
    
       i; j
    
      ++
    
      )
 
    
      if
    
       (i 
    
      %
    
       prime[j] 
    
      ==
    
       
    
      0
    
      )
 {
 ok 
    
      =
    
       
    
      false
    
      ;
 
    
      break
    
      ;
 }
 
    
      if
    
       (ok)
 {
 prime[primenum
    
      ++
    
      ] 
    
      =
    
       i;
 }
 }
}


    
      void
    
       init()
{
 memset(cost, 
    
      -
    
      1
    
      , 
    
      sizeof
    
      (cost));
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       
    
      4
    
      ; i
    
      ++
    
      )
 {
 
    
      char
    
       ch;
 scanf(
    
      "
    
      %c
    
      "
    
      , 
    
      &
    
      ch);
 a.num[i] 
    
      =
    
       ch 
    
      -
    
       
    
      '
    
      0
    
      '
    
      ;
 }
 getchar();
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       
    
      4
    
      ; i
    
      ++
    
      )
 {
 
    
      char
    
       ch;
 scanf(
    
      "
    
      %c
    
      "
    
      , 
    
      &
    
      ch);
 b.num[i] 
    
      =
    
       ch 
    
      -
    
       
    
      '
    
      0
    
      '
    
      ;
 }
 getchar();
}


    
      bool
    
       isprime(
    
      int
    
       a)
{
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       primenum 
    
      &&
    
       prime[i] 
    
      *
    
       prime[i] 
    
      <=
    
       a; i
    
      ++
    
      )
 
    
      if
    
       (a 
    
      %
    
       prime[i] 
    
      ==
    
       
    
      0
    
      )
 
    
      return
    
       
    
      false
    
      ;
 
    
      return
    
       
    
      true
    
      ;
}


    
      void
    
       work()
{
 cost[toint(a)] 
    
      =
    
       
    
      0
    
      ;
 queue
    
      <
    
      item
    
      >
    
       q;
 q.push(a);
 
    
      while
    
       (
    
      !
    
      q.empty())
 {
 item temp 
    
      =
    
       q.front();
 
    
      int
    
       costnow 
    
      =
    
       cost[toint(temp)];
 q.pop();
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       
    
      4
    
      ; i
    
      ++
    
      )
 {
 
    
      int
    
       x 
    
      =
    
       temp.num[i];
 
    
      for
    
       (
    
      int
    
       j 
    
      =
    
       
    
      0
    
      ; j 
    
      <
    
       
    
      10
    
      ; j
    
      ++
    
      )
 {
 
    
      if
    
       (i 
    
      ==
    
       
    
      0
    
       
    
      &&
    
       j 
    
      ==
    
       
    
      0
    
      )
 
    
      continue
    
      ;
 
    
      if
    
       (j 
    
      ==
    
       x)
 
    
      continue
    
      ;
 temp.num[i] 
    
      =
    
       j;
 
    
      int
    
       inttemp 
    
      =
    
       toint(temp);
 
    
      if
    
       (cost[inttemp] 
    
      ==
    
       
    
      -
    
      1
    
       
    
      &&
    
       isprime(inttemp))
 {
 cost[inttemp] 
    
      =
    
       costnow 
    
      +
    
       
    
      1
    
      ;
 
    
      if
    
       (inttemp 
    
      ==
    
       toint(b))
 {
 printf(
    
      "
    
      %d\n
    
      "
    
      , cost[inttemp]);
 
    
      return
    
      ;
 }
 q.push(temp);
 }
 }
 temp.num[i] 
    
      =
    
       x;
 }
 }
}


    
      int
    
       main()
{
 
    
      //
    
      freopen("D:\\t.txt", "r", stdin);
    
      

    
       
    
      int
    
       t;
 makeprime();
 scanf(
    
      "
    
      %d
    
      "
    
      , 
    
      &
    
      t);
 getchar();
 
    
      while
    
       (t
    
      --
    
      )
 {
 init();
 
    
      if
    
       (toint(a) 
    
      ==
    
       toint(b))
 printf(
    
      "
    
      0\n
    
      "
    
      );
 work();
 }
 
    
      return
    
       
    
      0
    
      ;
}