# Light OJ 1141 – Number Transformation

```
/*
+-+ +-+ +-+
|R| |.| |S|
+-+ +-+ +-+
*/

#include &lt;bits/stdc++.h&gt;

#define pii             pair &lt;int,int&gt;
#define sc              scanf
#define pf              printf
#define Pi              2*acos(0.0)
#define ms(a,b)         memset(a, b, sizeof(a))
#define pb(a)           push_back(a)
#define MP              make_pair
#define db              double
#define ll              long long
#define EPS             10E-10
#define ff              first
#define ss              second
#define sqr(x)          (x)*(x)
#define D(x)            cout&lt;&lt;#x &quot; = &quot;&lt;&lt;(x)&lt;&lt;endl
#define VI              vector &lt;int&gt;
#define DBG             pf(&quot;Hi\n&quot;)
#define MOD             100007
#define MAX             10000
#define CIN             ios_base::sync_with_stdio(0); cin.tie(0)
#define SZ(a)           (int)a.size()
#define sf(a)           scanf(&quot;%d&quot;,&amp;a)
#define sff(a,b)        scanf(&quot;%d%d&quot;,&amp;a,&amp;b)
#define sfff(a,b,c)     scanf(&quot;%d%d%d&quot;,&amp;a,&amp;b,&amp;c)
#define loop(i,n)       for(int i=0;i&lt;n;i++)
#define REP(i,a,b)      for(int i=a;i&lt;b;i++)
#define TEST_CASE(t)    for(int z=1;z&lt;=t;z++)
#define PRINT_CASE      printf(&quot;Case %d: &quot;,z)
#define all(a)          a.begin(),a.end()
#define intlim          2147483648
#define inf             1000000
#define ull             unsigned long long

using namespace std;

vector&lt;int&gt;v,factor;
bool prime[1100];

void sieve()
{
prime[0]=1;
for(int i=2; i&lt;1100;)
{
v.pb(i);
for(int j=i+i; j&lt;1100; j+=i)
prime[j]=1;
for(++i;; i++)
if(!prime[i])
break;
}
}

int d[1110];

bool visited[1110];

int bfs(int src, int dst)
{
d[src]=0;
queue&lt;int&gt;Q;
Q.push(src);
visited[src]=1;
while(!Q.empty())
{
int u=Q.front();
Q.pop();
if(u==dst) return d[u];
int temp=u;
if(prime[u]==0) continue;
for(int i=0; temp&gt;1; i++)
{
if(temp%v[i]==0)
{
factor.pb(v[i]);
while(temp%v[i]==0)
temp/=v[i];
}
}

for(int i=0; i&lt;SZ(factor); i++)
{
int v=u+factor[i];
if(v&lt;=dst &amp;&amp; !visited[v])
{
visited[v]=1;
Q.push(v);
d[v]=d[u]+1;
}
}
factor.clear();
}
return -1;
}

void allclear()
{
ms(visited,0);
factor.clear();
ms(d,0);
}

int main()
{
///freopen(&quot;in.txt&quot;,&quot;r&quot;,stdin);
///freopen(&quot;out.txt&quot;,&quot;w&quot;,stdout);
sieve();

int t;
sf(t);
TEST_CASE(t)
{
allclear();
int a,b;
sff(a,b);
PRINT_CASE;
cout&lt;&lt;bfs(a,b)&lt;&lt;endl;
}
return 0;
}

```