寒假训练补题-第三天-H - 8-BFS（较易）

原题链接：http://poj.org/problem?id=3126
The ministers of the cabinet were quite upset by the message from the Chief of Security stating that they would all have to change the four-digit room numbers on their offices.
— It is a matter of security to change such things every now and then, to keep the enemy in the dark.
— But look, I have chosen my number 1033 for good reasons. I am the Prime minister, you know!
— I know, so therefore your new number 8179 is also a prime. You will just have to paste four new digits over the four old ones on your office door.
— No, it’s not that simple. Suppose that I change the first digit to an 8, then the number will read 8033 which is not a prime!
— I see, being the prime minister you cannot stand having a non-prime number on your door even for a few seconds.
— Correct! So I must invent a scheme for going from 1033 to 8179 by a path of prime numbers where only one digit is changed from one prime to the next prime.

**内阁部长对安全主任的信息感到非常不安，他们说他们都必须改变办公室的四位数房间号码。

• 不时地改变这些事情是为了安全，以便让敌人陷入黑暗。
• 但是看，我选择了我的号码1033是有充分理由的。
  你知道，我是总理！
• 我知道，所以你的新号码8179也是一个素数。
  您只需在办公室门上的四个旧数字上粘贴四个新数字即可。
• 不，这不是那么简单。
  假设我将第一个数字更改为8，那么数字将为8033，这不是素数！
• 我知道，作为总理，即使几秒钟，你也不能忍受门上的非素数。
• 正确！因此，我必须通过一个素数路径发明一个从1033到8179的方案，其中只有一个数字从一个素数变为下一个素数。**

Now, the minister of finance, who had been eavesdropping, intervened.
— No unnecessary expenditure, please! I happen to know that the price of a digit is one pound.
— Hmm, in that case I need a computer program to minimize the cost. You don’t know some very cheap software gurus, do you?
— In fact, I do. You see, there is this programming contest going on… Help the prime minister to find the cheapest prime path between any two given four-digit primes! The first digit must be nonzero, of course. Here is a solution in the case above.
1033
1733
3733
3739
3779
8779
8179
The cost of this solution is 6 pounds. Note that the digit 1 which got pasted over in step 2 can not be reused in the last step – a new 1 must be purchased.

**现在，一直在窃听的财政部长进行了干预。

• 请不要花费不必要的开支！
  我碰巧知道一个数字的价格是一磅。
• 嗯，在这种情况下，我需要一个计算机程序来降低成本。
  你不知道一些非常便宜的软件大师，对吗？
• 事实上，我这样做。
  你看，正在进行这个编程竞赛…帮助总理找到两个给定的四位数素数之间最便宜的素数路径！
  当然，第一个数字必须是非零的。
  这是上述情况的解决方案。
  1033
  1733
  3733
  3739
  3779
  8779
  8179
  该解决方案的成本为6磅。
  请注意，在步骤2中粘贴的数字1在最后一步中无法重复使用 - 必须购买新的1。**

Input
One line with a positive number: the number of test cases (at most 100). Then for each test case, one line with two numbers separated by a blank. Both numbers are four-digit primes (without leading zeros).

输入
一行带正数：测试用例数（最多100个）。
然后对于每个测试用例，一行用两个数字用空格分隔。
这两个数字都是四位数的素数（没有前导零）。

Output
One line for each case, either with a number stating the minimal cost or containing the word Impossible.

产量
每个案例一行，要么是一个说明最低成本的数字，要么包含“不可能”这个词。

Sample Input
3
1033 8179
1373 8017
1033 1033
Sample Output
6
7
0
ac代码：

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