POJ 3126 Prime Path（搜索）

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AC代码：
#include <iostream>#include <cstdio>#include <cmath>#include <cstring>#include <string>#include <queue>using namespace std;struct node{    int pos,t;    bool operator < (const node &a)const{        return t > a.t;    }};int prime[10005];int vis[10005];void is_prime(){    memset(prime,0,sizeof(prime));    for(int i = 1000; i < 10000; i++){        int tmp = sqrt(i*1.0),flag = 1;        for(int j = 2; j <= tmp; j++){            if(i%j == 0){                flag = 0;                break;            }        }        if(flag)            prime[i] = 1;    }}int bfs(int a,int b){    memset(vis,0,sizeof(vis));    node cur;    int num[4];    cur.pos = a;cur.t = 0;    vis[a] = 1;    priority_queue<node> q;    q.push(cur);    while(!q.empty()){        cur = q.top();        q.pop();        if(cur.pos == b){            return cur.t;        }        int tmppos = cur.pos;        for(int i = 3; i >= 0; i--,tmppos/=10){            num[i] = tmppos%10;        }        for(int i = 0; i < 4; i++){            int tmp = num[i];            for(int j = 0; j < 10; j++){                if(num[i] != j){                    num[i] = j;                    int pos = num[0]*1000+num[1]*100+num[2]*10+num[3];                    if(prime[pos] && !vis[pos]){                        vis[pos] = 1;                        q.push(node{pos,cur.t+1});                    }                }                num[i] = tmp;            }        }    }    return -1;}int main(){    is_prime();    int T;    scanf("%d",&T);    while(T--){        int a,b;        scanf("%d%d",&a,&b);        int ans = bfs(a,b);        if(ans < 0)            printf("Impossible\n");        else            printf("%d\n",ans);    }    return 0;}
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