HDU1973 http://acm.hdu.edu.cn/showproblem.php?pid=1973

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<queue>
#include<math.h>
#define N 10010

using namespace std;

int vis
;
char s1[5], s2[5], s3[5];

struct node
{
int step;
char st[5];
};

int prime(int y)
{
int i, k = (int)sqrt(y);
for(i = 2 ; i <= k ; i++)
if(y % i == 0)
return 0;
return 1;
}

int BFS(char s[])
{
queue<node>Q;
node now, next;
int i, j, h, x = 0;
memset(vis, 0, sizeof(vis));
memset(s3, 0, sizeof(s3));
for(i = 0 ; i < 4 ; i++)
x = x * 10 + (s[i] - '0');
vis[x] = 1;
strcpy(now.st, s);
now.step = 0;
Q.push(now);
while(!Q.empty())
{
now = Q.front();
Q.pop();
if(strcmp(now.st, s2) == 0)
return now.step;
for(i = 0 ; i < 4 ; i++)//各个位（即个位，十位，百位，千位）
{
for(j = 0 ; j < 10 ; j++)//0到9十个数
{
if(i == 0 && j == 0)//千位不为0
continue;
if(now.st[i] == j + '0')//原有的数不需要替换
continue;
strcpy(s3, now.st);
now.st[i] = j + '0';//0到9其中的一个数去替换四位数气中的一位
x = 0;
for(h = 0 ; h < 4 ; h++)
x = x * 10 + (now.st[h] - '0');
if(prime(x) == 1 && !vis[x])
{
vis[x] = 1;
next.step = now.step + 1;
strcpy(next.st, now.st);
i = 0;/***/
j = 0;/***/
Q.push(next);
}
strcpy(now.st, s3);
}
}
}
return -1;
}

int main()
{
int t;
scanf("%d", &t);
while(t--)
{
scanf("%s%s", s1, s2);
printf("%d\n", BFS(s1));
}
return 0;
}