LeetCode 864: Shortest Path to Get All Keys

Explanation:

To solve this problem, we can use a breadth-first search (BFS) algorithm to explore all possible paths from the starting point while considering the keys collected so far. We will keep track of the current position, keys collected, and the steps taken to reach that position in a state (position, keys), and use a queue to process states in a BFS manner.

1. Initialize a queue and a visited set to store visited states.
2. Start from the initial position of the starting point '@' and add it to the queue with an empty key set.
3. Perform BFS:
   • Pop a state (position, keys) from the queue.
   • Explore the four possible directions (up, down, left, right) from the current position.
   • If the new position is valid and not visited before:
     • If it is an empty cell '.' or a key, update the keys collected so far.
     • If it is a lock and the key required is not collected yet, skip this state.
     • Add the new state to the queue with updated position and keys, and increase the steps taken.
   • If all keys are collected, return the steps taken as the result.
4. If all possible states are explored and all keys are not collected, return -1.

:

class Solution {
    public int shortestPathAllKeys(String[] grid) {
        // Java solution
    }
}