poj 3126 Prime Path（bfs）

#include <cstdio>
#include <cstring>
#include <queue>
using std::queue;

struct node
{
int val;
int step;
};
bool prime[10000];
bool book[10000];
int s,e,res;
int num[4];

void getPrime()
{
memset(prime,0,sizeof(prime));
prime[0] = prime[1] = true;
for(int i = 2; i < 10000; ++i)
{
if(!prime[i])
for(int j = 2*i; j < 10000; j += i)
prime[j] = true;//false表示是素数，true表示不是素数
}
}

bool isPrime(int num)
{
return !prime[num];
}

void BFS()
{
memset(book,0,sizeof(book));
queue<node> que;
node head;
head.val = s;
head.step = 0;
book[s] = true;
que.push(head);
int temp;
while(!que.empty())
{
node cur = que.front();
que.pop();
if(cur.val == e)
{
res = cur.step;
return;
}
num[0] = cur.val/1000;
num[1] = (cur.val/100)%10;
num[2] = (cur.val/10)%10;
num[3] = cur.val%10;

for(int i = 0; i < 4; ++i)
{
temp = num[i];
for(int j = 0; j < 10; ++j)
{
if(i == 0 && j == 0) continue;
if(temp != j)
{
num[i] = j;
int n = num[0]*1000+num[1]*100+num[2]*10+num[3];
if(!book
&& isPrime(n))
{
node atp;
atp.val = n;
atp.step = cur.step + 1;
book
= true;
que.push(atp);
}
}
}
num[i] = temp;
}
}
}

int main()
{
int t;
getPrime();
scanf("%d",&t);
while(t--)
{
res = -1;
scanf("%d %d",&s,&e);
BFS();
if(res == -1)
printf("Impossible\n");
else
printf("%d\n",res);
}
return 0;
}