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# 909. Snakes and Ladders
"""
you are given an 'n x n' integer matrix 'board' where the cells are all
labeled from 1 to 'n^2' in 'boustropheden style' starting from bottom left of
the board, and alternating direction each row. a board square on row 'r' and
column 'c' has a snake of a ladder if 'board[r][c] != -1'. the destination of
that snake or ladder is 'board[r][c]'. squares 1 and 'n^2' are not the
starting points of any snake or ladder. note that you only take a snake or a
ladder at most once per dice roll. if the destination to a snake or ladder is
the start of another snake or ladder, you do not follow the subsequent snake
or ladder.
"""
class Solution(object):
def snakesAndLadders(self, board):
"""
:type board: List[List[int]]
:rtype: int
"""
n = len(board)
def coordinates(num):
row, col = (num - 1) // n, (num - 1) % n
col = n - 1 if row % 2 == 1 else col
row = n - 1 - row
return row, col
vis, queue = set(), [(1, 0)]
vis.add(1)
while queue:
curr, moves = queue.pop(0)
if curr == n**2:
return moves
for i in range(1, 7):
next = curr + i
if next > n**2:
continue
row, col = coordinates(next)
if board[row][col] != -1:
next = board[row][col]
if next == n**2:
return moves + 1
if next not in vis:
vis.add(next)
queue.append((next, moves + 1))
return -1
if __name__ == "__main__":
obj = Solution()
print(
obj.snakesAndLadders(
board=[
[-1, -1, -1, -1, -1, -1],
[-1, -1, -1, -1, -1, -1],
[-1, -1, -1, -1, -1, -1],
[-1, 35, -1, -1, 13, -1],
[-1, -1, -1, -1, -1, -1],
[-1, 15, -1, -1, -1, -1],
]
)
)
print(obj.snakesAndLadders(board=[[-1, -1], [-1, 3]]))
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