【POJ】3126

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http://poj.org/problem?id=3126

给定两个四位素数a 、 b，要求把a变换到b
每次只能变一个数，且变的这个数是素数，求最少变换次数。

素数表+bfs

#include <iostream>#include <cstdio>#include <cstring>#include <cmath>#include <queue>#include <algorithm>using namespace std;int n;int prime[10005];bool is[10005];int sieve(){    int sum=0;    memset(is,true,sizeof(is));    is[0]=is[1]=false;    for (int i=2;i<=10000;i++){        if (is[i]){            prime[sum++]=i;            for (int j=i*2;j<=10000;j+=i){                is[j]=false;            }        }    }    return sum;}int get_next(int number,int digit,int change){    switch(digit){        case 0: return number/10*10+change;        case 1: return number/100*100+number%10+change*10;        case 2: return number/1000*1000+number%100+change*100;        case 3: return number%1000 +change*1000;    }    return 0;}int f[10005];int main(){    sieve();    cin >> n;    while (n--){        int from,to;        cin >> from >> to;        memset(f,0x3f,sizeof(f));        f[from]=0;        queue <int> q;        q.push(from);        while (!q.empty()){            int now=q.front();            q.pop();            for (int i=0;i<4;i++){                for (int j=0;j<10;j++){                    if (i==3&&j==0) continue;                    int next=get_next(now,i,j);                    if (!is[next]||f[next]<=f[now]) continue;                    f[next]=f[now]+1;                    q.push(next);                }            }        }        cout << f[to] << endl;    }}

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