Valid Tic-Tac-Toe State
A Tic-Tac-Toe board is given as a string array board
. Return True if and only if it is possible to reach this board position during the course of a valid tic-tac-toe game.
The board
is a 3 x 3 array, and consists of characters " "
, "X"
, and "O"
. The " " character represents an empty square.
Here are the rules of Tic-Tac-Toe:
Players take turns placing characters into empty squares (" ").
The first player always places "X" characters, while the second player always places "O" characters.
"X" and "O" characters are always placed into empty squares, never filled ones.
The game ends when there are 3 of the same (non-empty) character filling any row, column, or diagonal.
The game also ends if all squares are non-empty.
No more moves can be played if the game is over.
Example 1:
Input: board = ["O ", " ", " "]
Output: false
Explanation: The first player always plays "X".
Example 2:
Input: board = ["XOX", " X ", " "]
Output: false
Explanation: Players take turns making moves.
Example 3:
Input: board = ["XXX", " ", "OOO"]
Output: false
Example 4:
Input: board = ["XOX", "O O", "XOX"]
Output: true
分析
h,v,l,r用Counter,可以用来存对角线 x-y 不用担心负数
存储4个方向累积数字和turn,Player1 ++Player -- 。最后比较是 == +n 还是-n
最后可能不合法结果
1 turn1 和win 0 或者win1 和turn 0
2 都win。
3 turn只能0,1
from collections import Counter
class Solution:
def validTicTacToe(self, board: List[str]) -> bool:
h, v, l, r = Counter(), Counter(), Counter(), Counter()
turn = 0
for i in range(3):
for j in range(3):
if board[i][j] == 'X' :
turn += 1
h[i] += 1
v[j] += 1
l[i + j] += 1
r[i - j] += 1
elif board[i][j] == 'O':
turn -= 1
h[i] -= 1
v[j] -= 1
l[i + j] -= 1
r[i - j] -= 1
xwin = owin = False
for i in range(3):
for j in range(3):
xwin |= h[i] == 3 or v[j] == 3 or l[i+j] == 3 or r[i-j] == 3
owin |= h[i] == -3 or v[j] == -3 or l[i+j] == -3 or r[i-j] == -3
if xwin and turn == 0 or owin and turn == 1 or turn not in {0,1} or xwin and owin:
return False
return True
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