36. 有效的数独
判断当前数独是否有效（不需要填充数独） 只要用3个二维数组维护9行、9列、9个九宫格。
class Solution:
def isValidSudoku(self, board: List[List[str]]) -> bool:
row = [[] * 9 for _ in range(9)]
col = [[] * 9 for _ in range(9)]
nine = [[] * 9 for _ in range(9)]
for i in range(len(board)):
for j in range(len(board[0])):
tmp = board[i][j]
if not tmp.isdigit():
continue
if (tmp in row[i]) or (tmp in col[j]) or (tmp in nine[(j // 3) * 3 + (i // 3)]):
return False
row[i].append(tmp)
col[j].append(tmp)
nine[(j // 3) * 3 + (i // 3)].append(tmp)
return True
73. 矩阵置零
如果一个元素为 0 ，则将其所在行和列的所有元素都设为 0 。请使用 原地 算法。 A： 利用数组的首行和首列来记录 0 值 另外用两个布尔值记录首行首列是否需要置0
class Solution:
def setZeroes(self, matrix: List[List[int]]) -> None:
"""
Do not return anything, modify matrix in-place instead.
"""
#标记
m,n = len(matrix), len(matrix[0])
row = any(x == 0 for x in matrix[0])
col = any(matrix[r][0] == 0 for r in range(m) )
for i in range(m):
for j in range(n):
if matrix[i][j] == 0:
matrix[i][0] = 0
matrix[0][j] = 0
#置零
for i in range(1,m):
for j in range(1,n):
if matrix[i][0] == 0 or matrix[0][j] == 0:
matrix[i][j] = 0
if row:
for j in range(0,n):
matrix[0][j] = 0
if col:
for i in range(0,m):
matrix[i][0] = 0
