773. Sliding Puzzle

On a 2x3 board, there are 5 tiles represented by the integers 1 through 5, and an empty square represented by 0.

A move consists of choosing 0 and a 4-directionally adjacent number and swapping it.

The state of the board is solved if and only if the board is [[1,2,3],[4,5,0]].

Given a puzzle board, return the least number of moves required so that the state of the board is solved. If it is impossible for the state of the board to be solved, return -1.

Examples:

Input: board = [[1,2,3],[4,0,5]]
Output: 1
Explanation: Swap the 0 and the 5 in one move.
Input: board = [[1,2,3],[5,4,0]]
Output: -1
Explanation: No number of moves will make the board solved.
Input: board = [[4,1,2],[5,0,3]]
Output: 5
Explanation: 5 is the smallest number of moves that solves the board.
An example path:
After move 0: [[4,1,2],[5,0,3]]
After move 1: [[4,1,2],[0,5,3]]
After move 2: [[0,1,2],[4,5,3]]
After move 3: [[1,0,2],[4,5,3]]
After move 4: [[1,2,0],[4,5,3]]
After move 5: [[1,2,3],[4,5,0]]
Input: board = [[3,2,4],[1,5,0]]
Output: 14

Note:

  • board will be a 2 x 3 array as described above.
  • board[i][j] will be a permutation of [0, 1, 2, 3, 4, 5].

Rust Solution

struct Solution;

use std::collections::HashSet;
use std::collections::VecDeque;

impl Solution {
    fn sliding_puzzle(board: Vec<Vec<i32>>) -> i32 {
        let mut visited: HashSet<Vec<i32>> = HashSet::new();
        let next = vec![
            vec![1, 3],
            vec![0, 4, 2],
            vec![1, 5],
            vec![0, 4],
            vec![3, 1, 5],
            vec![2, 4],
        ];
        let solved = vec![1, 2, 3, 4, 5, 0];
        let mut queue: VecDeque<(Vec<i32>, usize, i32)> = VecDeque::new();
        let mut line = vec![];
        board
            .into_iter()
            .for_each(|v| v.into_iter().for_each(|x| line.push(x)));
        let zero = line.iter().position(|&x| x == 0).unwrap();
        visited.insert(line.to_vec());
        queue.push_back((line, zero, 0));
        while let Some((line, zero, count)) = queue.pop_front() {
            if line == solved {
                return count;
            }
            for &index in &next[zero] {
                let mut copy = line.to_vec();
                copy.swap(index, zero);
                if visited.insert(copy.to_vec()) {
                    queue.push_back((copy, index, count + 1));
                }
            }
        }
        -1
    }
}

#[test]
fn test() {
    let board = vec_vec_i32![[1, 2, 3], [4, 0, 5]];
    let res = 1;
    assert_eq!(Solution::sliding_puzzle(board), res);
    let board = vec_vec_i32![[1, 2, 3], [5, 4, 0]];
    let res = -1;
    assert_eq!(Solution::sliding_puzzle(board), res);
    let board = vec_vec_i32![[4, 1, 2], [5, 0, 3]];
    let res = 5;
    assert_eq!(Solution::sliding_puzzle(board), res);
    let board = vec_vec_i32![[3, 2, 4], [1, 5, 0]];
    let res = 14;
    assert_eq!(Solution::sliding_puzzle(board), res);
}

Having problems with this solution? Click here to submit an issue on github.