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#!/usr/bin/env python
knightMoveList = [
[-2, -1], [-2, +1], [-1, -2], [-1, +2],
[+2, -1], [+2, +1], [+1, -2], [+1, +2],
]
def knightMoves(coordinates):
letter = coordinates[0:1]
num = int(coordinates[1:])
endpoints = []
for colRow in knightMoveList:
col, row = colRow
newcol = chr(ord(letter) + col)
if "a" <= newcol <= "h":
newrow = num + row
if 1 <= newrow <= 8:
endpoints.append(newcol + str(newrow))
return endpoints
def leastMoves(start, end):
# trivial case: we're already at the end point
if start == end:
return ( 0, end )
# Ok, we're going to need to search for a solution.
# Keep track of how many moves it takes to get to
# a particular position, starting at $start
moves = { start: 0 }
# also keep track of the path to get there
path_to = { start: start }
# make a queue of starting points
queue = [ start ]
while ( queue ):
start = queue.pop(0)
# figure out the valid moves that we haven't been to yet
endpoints = [
m for m in knightMoves(start) if m not in path_to
]
for next in endpoints:
# build the path to the next endpoint
path_to[next] = f'{path_to[start]} -> {next}'
# increment the number of moves it takes to get there
moves[next] = moves[start] + 1
# have we arrived at our destination
if next == end:
return ( moves[next], path_to[next] )
# no? then push this space onto our processing queue
queue.append(next)
# we can't get there from here!
# (only possible when the chessboard is an odd size)
return ( -1, "no path found" )
def solution(start, end):
print(f'Input: $start = \'{start}\', $end = \'{end}\'')
count, moves = leastMoves(start, end)
print(f'Output: {count}\n\n{moves}\n')
print('Example 1:')
solution('g2', 'a8')
print('\nExample 2:')
solution('g2', 'h2')
print('\nExample 3:')
solution('a1', 'h8')
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