public int openLockBFS(String[] deadends, String target) {

HashSet<String> dead = new HashSet<String>(Arrays.asList(deadends));

HashSet<String> vis = new HashSet<String>();

int level = 0, size;

Queue<String> q = new LinkedList<String>();

q.add("0000");

vis.add("0000");

StringBuilder sb;

char c;

while (!q.isEmpty()) {

size = q.size();

for (int i = 0; i < size; ++i) {

String s = q.poll();

if (target.equals(s))

return level;

if (dead.contains(s))

continue;

sb = new StringBuilder(s);

for (int j = 0; j < 4; ++j) {

c = sb.charAt(j);

String s1 = sb.substring(0, j) + (c == '9' ? 0 : c - '0' + 1) + sb.substring(j + 1);

String s2 = sb.substring(0, j) + (c == '0' ? 9 : c - '0' - 1) + sb.substring(j + 1);

if (!vis.contains(s1) && !dead.contains(s1)) {

q.add(s1);

vis.add(s1);

}

if (!vis.contains(s2) && !dead.contains(s2)) {

q.add(s2);

vis.add(s2);

}

}

}

level++;

}

return -1;

}