Algorithm
Problem Name: 752. Open the Lock
You have a lock in front of you with 4 circular wheels. Each wheel has 10 slots: '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'. The wheels can rotate freely and wrap around: for example we can turn '9' to be '0', or '0' to be '9'. Each move consists of turning one wheel one slot.
The lock initially starts at '0000', a string representing the state of the 4 wheels.
You are given a list of deadends dead ends, meaning if the lock displays any of these codes, the wheels of the lock will stop turning and you will be unable to open it.
Given a target representing the value of the wheels that will unlock the lock, return the minimum total number of turns required to open the lock, or -1 if it is impossible.
Example 1:
Input: deadends = ["0201","0101","0102","1212","2002"], target = "0202" Output: 6 Explanation: A sequence of valid moves would be "0000" -> "1000" -> "1100" -> "1200" -> "1201" -> "1202" -> "0202". Note that a sequence like "0000" -> "0001" -> "0002" -> "0102" -> "0202" would be invalid, because the wheels of the lock become stuck after the display becomes the dead end "0102".
Example 2:
Input: deadends = ["8888"], target = "0009" Output: 1 Explanation: We can turn the last wheel in reverse to move from "0000" -> "0009".
Example 3:
Input: deadends = ["8887","8889","8878","8898","8788","8988","7888","9888"], target = "8888" Output: -1 Explanation: We cannot reach the target without getting stuck.
Constraints:
1 <= deadends.length <= 500deadends[i].length == 4target.length == 4- target will not be in the list
deadends. targetanddeadends[i]consist of digits only.
Code Examples
#1 Code Example with Java Programming
Code -
Java Programming
class Solution {
public int openLock(String[] deadends, String target) {
Set deadEndSet = new HashSet<>(Arrays.asList(deadends));
if (deadEndSet.contains(target) || deadEndSet.contains("0000")) {
return -1;
}
Queue < String> queue = new LinkedList<>();
Set seen = new HashSet<>();
queue.add("0000");
seen.add("0000");
int steps = 0;
int[] rotations = {-1, 1};
while (!queue.isEmpty()) {
int size = queue.size();
for (int i = 0; i < size; i++) {
String removed = queue.remove();
if (removed.equals(target)) {
return steps;
}
if (deadEndSet.contains(removed)) {
continue;
}
for (int j = 0; j < 4; j++) {
for (int rotation : rotations) {
int changedVal = ((removed.charAt(j) - '0') + rotation + 10) % 10;
String newRotation = new StringBuilder()
.append(removed.substring(0,j)) .append(changedVal)
.append(removed.substring(j + 1))
.toString();
if (!seen.contains(newRotation)) {
seen.add(newRotation);
queue.add(newRotation);
}
}
}
}
steps++;
}
return -1;
}
}
Input
Output
#2 Code Example with Javascript Programming
Code -
Javascript Programming
const openLock = function(deadends, target, count = 0) {
let deadSet = new Set(deadends);
let visited = new Set();
if (deadSet.has("0000")) {
return -1;
}
let q = [];
q.push("0000");
visited.add("0000");
let steps = 0;
while (q.length > 0) {
let len = q.length;
for (let j = 0; j < len; j++) {
let cur = q.shift();
for (let i = 0; i < 4; i++) {
let slot = parseInt(cur[i]);
let before = cur.substr(0, i);
let after = cur.substr(i + 1);
let left = (10 + slot - 1) % 10;
let leftCode = before + left + after;
if (!visited.has(leftCode) && !deadSet.has(leftCode)) {
if (leftCode === target) {
return steps + 1;
}
visited.add(leftCode);
q.push(leftCode);
}
let right = (10 + slot + 1) % 10;
let rightCode = before + right + after;
if (!visited.has(rightCode) && !deadSet.has(rightCode)) {
if (rightCode === target) {
return steps + 1;
}
visited.add(rightCode);
q.push(rightCode);
}
}
}
steps++;
}
return -1;
};
Input
Output
#3 Code Example with Python Programming
Code -
Python Programming
class Solution:
def openLock(self, deadends, target):
moved, q, cnt, move = set(deadends), ["0000"], 0, {str(i): [str((i + 1) % 10), str((i - 1) % 10)] for i in range(10)}
if "0000" in moved:
return -1
while q:
new = []
cnt += 1
for s in q:
for i, c in enumerate(s):
for cur in (s[:i] + move[c][0] + s[i + 1:], s[:i] + move[c][1] + s[i + 1:]):
if cur not in moved:
if cur == target:
return cnt
new.append(cur)
moved.add(cur)
q = new
return -1
Input
Output