Light-oj-1141 .cpp

#include "bits/stdc++.h"
using namespace std;

int prime[]={2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67,

 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149,

151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229,

 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311,

313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401,

 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487,

491, 499, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571, 577, 587, 593,

599, 601, 607, 613, 617, 619, 631, 641, 643, 647, 653, 659, 661, 673, 677,

 683, 691, 701, 709, 719, 727, 733, 739, 743, 751, 757, 761, 769, 773,

787, 797, 809, 811, 821, 823, 827, 829, 839, 853, 857, 859, 863, 877, 881,

 883, 887, 907, 911, 919, 929, 937, 941, 947, 953, 967, 971, 977, 983, 991, 997};

int visited[1100];


int bfs(int s,int t){
    queue< pair<int,int> >Q;
    Q.push(make_pair(s,0));
    visited[s]=1;
    while(!Q.empty()){
        int u=Q.front().first;
        int time=Q.front().second;
        Q.pop();
        visited[u]=1;
        if(u==t)return time;
        if(u<t){
            for(int i=0; prime[i]<u; i++){
                if((!visited[prime[i]+u])&&(u+prime[i]<=t)&&(u%prime[i]==0)){
                    Q.push(make_pair(u+prime[i],time+1));
                }
            }
        }
    }
    return -1;
}

int main(){
    int t,cs=1;
    scanf("%d",&t);
    while(t--){
        int s,t;
        memset(visited,0,sizeof(visited));
        scanf("%d %d",&s,&t);
        printf("Case %d: %d\n",cs++,bfs(s,t));
    }
    return 0;
}