POJ3126

//  1：376K 204ms
#include <iostream>
#include <queue>
using namespace std;

#define SIZE 10000
int prim[SIZE];
int dist[SIZE];
int visit[SIZE];
int primSize;

void prime()
{
	int i,j;
	bool mark = false;
	int temp[SIZE];
	memset(temp, 0,sizeof(temp));
	primSize = 0;
	for ( i = 2; i < SIZE; i++ )
	{
		if ( !temp[i] ){
			for ( j = 2; j*i < SIZE; j++ )
				temp[j*i] = -1;
			if ( i > 1000  )
				prim[++primSize] = i;
		}
				}
}

bool isAdjacent( int curr, int next )
{
	int change = 0;
	if ( curr%10 == next%10 ) change++;
	if ( (curr/10)%10 == (next/10)%10 ) change++;
	if ( (curr/100)%10 == (next/100)%10 ) change++;
	if ( curr/1000 == next/1000 ) change++;
	return change == 3;
}

int bfs( int start, int end )
{
	queue<int> Q;
	int i,v;
	bool isFind = false;
	
	memset(visit,0,sizeof(visit));
	memset(dist,0,sizeof(dist));
	
	dist[start] = 0;
	visit[start] = 1;
	Q.push(start);
	
	while( !Q.empty() )
	{
		v = Q.front();
		Q.pop();
						  
		for (i = 1; i <= primSize && !isFind; i++ ) 
						  {
			if( !visit[prim[i]] )
			{
				if ( isAdjacent(prim[i], v) )
				{
					dist[prim[i]] = dist[v] + 1;
					visit[prim[i]] = 1;
					Q.push(prim[i]);
					if ( prim[i] == end )
						isFind = true; 
				}
			}
						  }
	}
	if ( !dist[end] ) 
		return -1;
	else return dist[end];
}
int main()
{
	int n,first,second,ans;
	
	prime();
	
	cin >> n;
	while( n-- )
	{
		cin >> first >> second;
		if ( first == second ) {
			cout << "0" << endl;
			continue;
		}
		ans = bfs( first, second );
		if ( ans < 0 ) cout << "Impossible" << endl;
		else cout << ans << endl;
	}
	return 0;
}
//  2：344K 32ms
#include <iostream>
#include <queue>
using namespace std;

#define SIZE 10000
int prim[SIZE];
int dist[SIZE];
bool visit[SIZE];

void prime()
{
	int i,j;
	
	memset(prim,0,sizeof(prim));
	for ( i = 2; i < SIZE; i++ )
	{
		if ( !prim[i] ){
			for ( j = 2; j*i < SIZE; j++ )
				prim[j*i] = 1;
		}
	}
}

int bfs( int start, int end )
{
	queue<int> Q;
	int i,j,v,temp;
	bool isFind = false;
	
	memset(visit,false,sizeof(visit));
	memset(dist,0,sizeof(dist));
		  
	dist[start] = 0;
	visit[start] = true;
	Q.push(start);
		  
	while( !Q.empty() )
	{
		v = Q.front();
		Q.pop();
		
		char curr[4];  sprintf(curr,"%d",v);
		
		for ( i = 0; i < 4 && !isFind; i++ )
		{
			for ( j = 0; j < 10 && !isFind; j++ )
			{
				if ( !i && !j ) continue;
				else if ( i == 0 )
					temp = 1000*j+100*(curr[1]-'0')+10*(curr[2]-'0')+(curr[3]-'0');
				else if ( i == 1 )
					temp = 1000*(curr[0]-'0')+100*j+10*(curr[2]-'0')+(curr[3]-'0');
				else if ( i == 2 )
					temp = 1000*(curr[0]-'0')+100*(curr[1]-'0')+10*j+(curr[3]-'0');
				else 
					temp = 1000*(curr[0]-'0')+100*(curr[1]-'0')+10*(curr[2]-'0')+j;
				
				if ( !visit[temp] && !prim[temp] )
				{
					dist[temp] = dist[v] + 1;
					visit[temp] = true;
					Q.push(temp);
					if ( temp == end )
						isFind = true;
				}
			} 
		}
	}
	if ( !dist[end] ) 
		return -1;
	else return dist[end];
}


int main()
{
	int n,first,second,ans;
	
	prime();
	
	cin >> n;
	while( n-- )
	{
		cin >> first >> second;
		if ( first == second ) {
			cout << "0" << endl;
			continue;
		}
		ans = bfs( first, second );
		if ( ans < 0 ) cout << "Impossible" << endl;
		else cout << ans << endl;
	}
	return 0;
}