Foobar Google Challenge - Don't Get Volunteered

Challenge3.py

"""
Don't Get Volunteered!
======================

As a henchman on Commander Lambda's space station, you're expected to be resourceful, smart, and a quick thinker. It's not easy building a doomsday device and ordering the bunnies around at the same time, after all! In order to make sure that everyone is sufficiently quick-witted, Commander Lambda has installed new flooring outside the henchman dormitories. It looks like a chessboard, and every morning and evening you have to solve a new movement puzzle in order to cross the floor. That would be fine if you got to be the rook or the queen, but instead, you have to be the knight. Worse, if you take too much time solving the puzzle, you get "volunteered" as a test subject for the LAMBCHOP doomsday device!

To help yourself get to and from your bunk every day, write a function called solution(src, dest) which takes in two parameters: the source square, on which you start, and the destination square, which is where you need to land to solve the puzzle.  The function should return an integer representing the smallest number of moves it will take for you to travel from the source square to the destination square using a chess knight's moves (that is, two squares in any direction immediately followed by one square perpendicular to that direction, or vice versa, in an "L" shape).  Both the source and destination squares will be an integer between 0 and 63, inclusive, and are numbered like the example chessboard below:

-------------------------
| 0| 1| 2| 3| 4| 5| 6| 7|
-------------------------
| 8| 9|10|11|12|13|14|15|
-------------------------
|16|17|18|19|20|21|22|23|
-------------------------
|24|25|26|27|28|29|30|31|
-------------------------
|32|33|34|35|36|37|38|39|
-------------------------
|40|41|42|43|44|45|46|47|
-------------------------
|48|49|50|51|52|53|54|55|
-------------------------
|56|57|58|59|60|61|62|63|
-------------------------

Languages
=========

To provide a Python solution, edit solution.py
To provide a Java solution, edit Solution.java

Test cases
==========
Your code should pass the following test cases.
Note that it may also be run against hidden test cases not shown here.

-- Python cases --
Input:
solution.solution(0, 1)
Output:
    3

Input:
solution.solution(19, 36)
Output:
    1

-- Java cases --
Input:
Solution.solution(19, 36)
Output:
    1

Input:
Solution.solution(0, 1)
Output:
    3
"""

import heapq
from collections import defaultdict

BOARD_SIZE      = 8
BOARD_MOVEMENTS = [(1, 2), (1, -2), (-1, 2), (-1, -2),
                   (2, 1), (2, -1), (-2, 1), (-2, -1)]

class Node:
    def __init__(self, x, y, distance=0):
        self.x = x
        self.y = y
        self.distance = distance
    def __hash__(self):
        return hash(tuple(self))
    def __iter__(self):
        for i in [self.x, self.y]:
            yield i
    def __eq__(self, node):
        return self.x == node.x and self.y == node.y
    def __lt__(self, other):
        return self.x < node.x or (self.x == node.x and self.y < node.y)
    def __str__(self):
        return "<Node (x=%d, y=%d, d=%.02f)>" % (self.x, self.y, self.distance)
    def __repr__(self):
        return self.__str__()

class Board:
    def __init__(self, size, movements):
        self.size = size
        self.movements = movements
    def node(self, position):
        return Node(int(position % self.size) + 1, int(position / self.size) + 1)
    def valid(self, x, y):
        return True if x >= 0 < self.size and y >= 0 < self.size else False
    def distance(self, start, end):
        queue = []
        queue.append(start)
        visited = {}
        while queue:
            node = queue.pop(0)
            if node == end: return node.distance
            if node not in visited: 
                visited[node] = True
                for offset in self.movements:
                    x, y = list(tuple(x + y for x, y in zip(tuple(node), offset)))
                    if self.valid(x, y): queue.append(Node(x, y, node.distance + 1))

        return float('inf')

def solution(src, dest):
    chessboard = Board(size = BOARD_SIZE, movements = BOARD_MOVEMENTS)
    start = chessboard.node(src)
    end = chessboard.node(dest)
    distance = chessboard.distance(start, end)
    return distance