Solves the problem: "Given an origin and a destination on an empty chessboard, count how many moves are necessary for the rook to go from one to the other."

Solver.java

package org.rooksolver;

/**
 * Created by le-doude on 14/06/16.
 */
public class Solver {


    static final byte[][] moves = new byte[64][64];

    static final boolean[] isBlackSquare = {
            true, false, true, false, true, false, true, false,
            false, true, false, true, false, true, false, true,
            true, false, true, false, true, false, true, false,
            false, true, false, true, false, true, false, true,
            true, false, true, false, true, false, true, false,
            false, true, false, true, false, true, false, true,
            true, false, true, false, true, false, true, false,
            false, true, false, true, false, true, false, true,
    };

    static {
        for (int i = 0; i < 64; i++) {
            moves[i][i] = 0; //same square
            for (int j = i + 1; j < 64; j++) {
                if (moves[i][j] == 0) {
                    if (isBlackSquare[i] != isBlackSquare[j]) {//is on same color
                        moves[i][j] = moves[j][i] = -1; //not reachable
                    } else {
                        moves[i][j] = moves[j][i] = (byte) (isOnDiagonal(i, j) ? 1 : 2); //reachable since on same color
                    }
                }
            }
        }
    }

    //i always lesser than j
    private static boolean isOnDiagonal(int i, int j) {
        for (int k = i; k < 64; k+=7) {
            if(isBlackSquare[j] != isBlackSquare[k]) {
                break; //we have gone over the border.
            }
            if (k == j) {
                return true;
            }
        }
        for (int k = i; k < 64; k += 9) {
            if(isBlackSquare[j] != isBlackSquare[k]) {
                break; //we have gone over the border.
            }
            if (k == j) {
                return true;
            }
        }
        return false;
    }

    public static int countMovesForRook(int from, int to) {
        if (0 <= from && from < 64 && 0 <= to && to < 64) {
            return moves[from][to];
        } else {
            return -1;
        }
    }

    public static int countMovesForRook(int X, int Y, int x, int y) {
        if (0 <= X && X < 8 && 0 <= Y && Y < 8 && 0 <= x && x < 8 && 0 <= y && y < 8) {
            return countMovesForRook((X * 8) + Y, (x * 8) + y);
        } else {
            return -1;
        }
    }
}

This was a problem that was given to me during an interview at a very important company. On the moment I had a pure head-fart and couldn't even think of a most basic solution.
Actually the problem is very easy once you identify all 4 possible answers. Good training.

NB: isBlackSquare can be done with the function ((x / 8) % 2) == (x % 2)