水题：直接判断素数+bfs
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <sstream> 5 #include <algorithm> 6 #include <list> 7 #include <map> 8 #include <vector> 9 #include <queue> 10 #include <stack> 11 #include <cmath> 12 #include <cstdlib> 13 //#include <memory.h> 14 #define clc(a,b) memset(a,b,sizeof(a)) 15 using namespace std; 16 const int maxn=100000; 17 const int inf=0x3f3f3f3f; 18 int n,m; 19 bool pri[10000],vis[10000]; 20 int countt[10000]; 21 int t[4]; 22 void prim(){ 23 for(int i=1000;i<10000;i++){ 24 bool flag=false; 25 for(int j=2;j<i;j++) 26 if(i%j==0){ 27 pri[i]=false; 28 flag=true; 29 break; 30 } 31 if(!flag) 32 pri[i]=true; 33 } 34 } 35 36 int dfs(int a,int b){ 37 queue<int>q; 38 q.push(a); 39 vis[a]=true; 40 countt[a]=0; 41 while(!q.empty()){ 42 int v=q.front(); 43 q.pop(); 44 if(v==b){ 45 return countt[v]; 46 } 47 t[0]=v/1000; 48 t[1]=v%1000/100; 49 t[2]=v%100/10; 50 t[3]=v%10; 51 for(int i=0;i<4;i++){ 52 int tem=t[i]; 53 for(int j=0;j<10;j++){ 54 if(j!=tem){ 55 t[i]=j; 56 int vtemp=t[0]*1000+t[1]*100+t[2]*10+t[3]; 57 if(pri[vtemp]&&!vis[vtemp]){ 58 countt[vtemp]=countt[v]+1; 59 vis[vtemp]=true; 60 q.push(vtemp); 61 } 62 if(vtemp==b){ 63 return countt[vtemp]; 64 } 65 } 66 } 67 t[i]=tem; 68 } 69 } 70 return -1; 71 } 72 int main(){ 73 // freopen("in.txt","r",stdin); 74 int ans; 75 int T; 76 while(~scanf("%d",&T)){ 77 prim(); 78 while(T--){ 79 scanf("%d%d",&n,&m); 80 clc(vis,false); 81 clc(countt,0); 82 ans=dfs(n,m); 83 if(ans!=-1) 84 printf("%d ",ans); 85 else 86 printf("Impossible "); 87 } 88 } 89 return 0; 90 }