Prison Cells After N Days

There are 8 prison cells in a row, and each cell is either occupied or vacant.

Each day, whether the cell is occupied or vacant changes according to the following rules:

If a cell has two adjacent neighbors that are both occupied or both vacant, then the cell becomes occupied.
Otherwise, it becomes vacant.

(Note that because the prison is a row, the first and the last cells in the row can't have two adjacent neighbors.)

We describe the current state of the prison in the following way: cells[i] == 1 if the i-th cell is occupied, else cells[i] == 0.

Given the initial state of the prison, return the state of the prison after N days (and N such changes described above.)

Example 1:

Input: cells = [0,1,0,1,1,0,0,1], N = 7
Output: [0,0,1,1,0,0,0,0]
Explanation: 
The following table summarizes the state of the prison on each day:
Day 0: [0, 1, 0, 1, 1, 0, 0, 1]
Day 1: [0, 1, 1, 0, 0, 0, 0, 0]
Day 2: [0, 0, 0, 0, 1, 1, 1, 0]
Day 3: [0, 1, 1, 0, 0, 1, 0, 0]
Day 4: [0, 0, 0, 0, 0, 1, 0, 0]
Day 5: [0, 1, 1, 1, 0, 1, 0, 0]
Day 6: [0, 0, 1, 0, 1, 1, 0, 0]
Day 7: [0, 0, 1, 1, 0, 0, 0, 0]

Example 2:

Input: cells = [1,0,0,1,0,0,1,0], N = 1000000000
Output: [0,0,1,1,1,1,1,0]

Note:

cells.length == 8
cells[i] is in {0, 1}
1 <= N <= 10^9

Solution:

class Solution {
    public int[] prisonAfterNDays(int[] cells, int N) {
        List<int[]> list = new ArrayList();
        Set<Integer> set = new HashSet();
        int[] curr = cells.clone();
        // list.add(curr);
        while (true) {
            curr = getNext(curr);
            if (set.add(getHash(curr))) {
                list.add(curr);
            } else {
                break;
            }
        }
        // for (int[] arr : list) {
        //     System.out.println(Arrays.toString(arr));
        // }
        int n = (N - 1) % list.size();
        return list.get(n);
    }
    
    private int[] getNext(int[] curr) {
        int[] arr = new int[8];
        for (int i = 1; i < 7; i ++) {
            if (curr[i - 1] == curr[i + 1]) {
                arr[i] = 1;
            }
        }
        return arr;
    }
    
    private int getHash(int[] curr) {
        int hash = 0;
        for (int i = 0; i < 8; i ++) {
            hash = hash * 10 + curr[i];
        }
        return hash;
    }
}