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Open the Lock

Challenge Points: 20

Level: Medium

You are standing in front of a lock with 4 rotating wheels, each numbered from '0' to '9'.
Each wheel can rotate forward or backward by one step, and it wraps around (e.g., '9' → '0' or '0' → '9').

Your lock starts at "0000".
You are given a list of deadends — if the lock shows any of these combinations, it becomes stuck and can’t move further.

Your task is to find the minimum number of wheel turns required to reach the target combination.
If the target cannot be reached, return -1.

Example 1:

Input: deadends = ["0201","0101","0102","1212","2002"], target = "0202"

Output: 6

Explanation:

One valid path is: "0000" → "1000" → "1100" → "1200" → "1201" → "1202" → "0202".

Example 2:

Input: deadends = ["8888"], target = "0009"

Output: 1

Explanation:

Rotate the last wheel once: "0000" → "0009".

Example 3:

Input: deadends = ["8887","8889","8878","8898","8788","8988","7888","9888"], target = "8888"

Output: -1

Explanation:

All possible paths lead to deadends, so it’s impossible to unlock.

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