SnakesAndLadders.java

package graph;

import java.util.LinkedList;
import java.util.Queue;

public class SnakesAndLadders {

    public int snakesAndLadders(int[][] board) {
        int n = board.length, end = n * n, result = 0;

        Queue<Integer> q = new LinkedList<>();
        q.add(1);

        while (!q.isEmpty()) {
            result++;
            int size = q.size();

            while (size-- > 0) {
                int curr = q.poll();

                for (int i = 1; i <= 6; i++) {
                    int next = curr + i;
                    int[] rc = getRowCol(next, n);

                    next = board[rc[0]][rc[1]] == -1 ? next : board[rc[0]][rc[1]];
                    if (next == -2) continue;
                    if (next >= end) return result;

                    q.add(next);
                    board[rc[0]][rc[1]] = -2;
                }
            }
        }
        return -1;
    }

    private int[] getRowCol(int num, int n) {
        num--;
        int r = n - 1 - num / n, c;

        if (((n - 1) & 1) == (r & 1)) {
            c = num % n;
        } else {
            c = n - num % n - 1;
        }
        return new int[]{r, c};
    }
}