# Poj Solution 3126

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

import java.io.BufferedInputStream;
import java.util.Scanner;
public class Main {

static boolean[] isPrime = Prime.getPrimes(10000);

public static void main(String[] args) {

Scanner scan = new Scanner(new BufferedInputStream(System.in));
int cas = scan.nextInt();
for (int i = 1; i <= cas; i++) {
int start = scan.nextInt();
int end = scan.nextInt();
boolean[] isVisited = new boolean[10000];
int[] step = new int[10000];
isVisited[start] = true;
while (!queue.isEmpty()) {
int current = queue.pop();
if (current == end) {
break;
}
for (int j = 0; j <= 9; j++) {
int next1 = getNext(1, j, current);
int next2 = getNext(2, j, current);
int next3 = getNext(3, j, current);
int next4 = getNext(4, j, current);
if (!isVisited[next1]) {
step[next1] = step[current] + 1;
isVisited[next1] = true;
}
if (!isVisited[next2]) {
step[next2] = step[current] + 1;
isVisited[next2] = true;
}
if (!isVisited[next3]) {
step[next3] = step[current] + 1;
isVisited[next3] = true;
}
if (!isVisited[next4]) {
step[next4] = step[current] + 1;
isVisited[next4] = true;
}
}
}
System.out.println(step[end]);
}
}

public static int getNext(int flag, int i, int current) {
int next = 0;
if (flag == 1) {
if (i == 0) {
return current;
}
next = current % 1000 + i * 1000;
}
if (flag == 2) {
int t = current / 1000;
next = t * 1000 + current % 1000 % 100 + i * 100;
}
if (flag == 3) {
int t = current / 100;
int tt = current % 10;
next = t * 100 + i * 10 + tt;
}
if (flag == 4) {
next = current / 10 * 10 + i;

}
if (!isPrime[next]) {
return current;
}
return next;
}
}

class Prime {

public static boolean[] getPrimes(int n) {
int i, j, k, x;
boolean[] a = new boolean[n];
n++;
n /= 2;
int[] b = new int[(n + 1) * 2];
a[2] = true;
a[3] = true;
for (i = 1; i <= 2 * n; i++) {
b[i] = 0;
}
for (i = 3; i <= n; i += 3) {
for (j = 0; j < 2; j++) {
x = 2 * (i + j) - 1;
while (b[x] == 0) {
a[x] = true;
for (k = x; k <= 2 * n; k += x) {
b[k] = 1;
}
}
}
}
return a;
}
}

```
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