1 #define bug(x) cout<<#x<<" is "<<x<<endl 2 #define IO std::ios::sync_with_stdio(0) 3 #include <bits/stdc++.h> 4 using namespace std; 5 typedef long long ll; 6 #define mk make_pair 7 #define pb push_back 8 const int inf=2147483647; 9 const int N=1e5+10; 10 int T,len; 11 int vis[N],ok[N]; 12 void gao(){ 13 for(int i=2;i<=N;i++){ 14 if(!vis[i]){ 15 for(int j=i*2;j<=N;j+=i){ 16 vis[j]=1; 17 } 18 } 19 } 20 } 21 char s[10],t[10]; 22 struct node{ 23 char x[6]; 24 int step=0; 25 bool operator < (const node &p)const{ 26 return step>p.step; 27 } 28 }; 29 30 int tf(char *x){ 31 int y=0; 32 for(int i=1;i<=len;i++){ 33 y*=10; 34 y+=x[i]-'0'; 35 } 36 return y; 37 } 38 39 40 41 int bfs(){ 42 for(int i=1000;i<N;i++){ 43 ok[i]=0; 44 } 45 priority_queue<node>q; 46 int x=tf(s); 47 int y=tf(t); 48 node now; 49 for(int i=1;i<=len;i++)now.x[i]=s[i]; 50 now.step=0; 51 q.push(now); 52 while(!q.empty()){ 53 now=q.top(); 54 q.pop(); 55 int f=0; 56 ok[tf(now.x)]=1; 57 for(int i=1;i<=len;i++){ 58 if(now.x[i]!=t[i]){ 59 f=1; 60 break; 61 } 62 } 63 if(!f)return now.step; 64 for(int i=1;i<=len;i++){ 65 for(int j='0';j<='9';j++){ 66 node next=now; 67 next.step=now.step+1; 68 next.x[i]=j; 69 int y=tf(next.x); 70 //bug(y); 71 if(!vis[y]&&!ok[y]){ 72 //printf("##%d ",y); 73 q.push(next); 74 } 75 } 76 77 } 78 } 79 return -1; 80 } 81 int main(){ 82 gao(); 83 scanf("%d",&T); 84 while(T--){ 85 scanf("%s %s",s+1,t+1); 86 len=strlen(s+1); 87 int x=tf(s); 88 int y=tf(t); 89 printf("%d ",bfs()); 90 } 91 } 92 /* 93 100 94 1009 1097 95 1021 1031 96 1009 1097 97 1033 1033 98 1021 1091 99 */