暴力回溯法可以解决，但是会超时
class Solution:
def exist(self, board: List[List[str]], word: str) -> bool:
visited = []
direction = [-1,0,1,0,-1]
m = len(board)
n = len(board[0])
def backTracking(start,idx):
if idx>=len(word):
return True
for i in range(4):
x = start[0] + direction[i]
y = start[1] + direction[i+1]
if 0<=x<m and 0<=y<n and (x,y) not in visited and board[x][y] == word[idx]:
visited.append((x,y))
if backTracking((x,y),idx+1):
return True
visited.pop()
return False
for i in range(m):
for j in range(n):
if board[i][j] == word[0]:
visited.append((i,j))
if backTracking((i,j),1):
return True
visited.pop()
else:
continue
return False然后通过把visited换成对board操作，成功通过
class Solution:
def exist(self, board: List[List[str]], word: str) -> bool:
direction = [-1,0,1,0,-1]
m = len(board)
n = len(board[0])
def backTracking(start,idx):
if idx>=len(word):
return True
for i in range(4):
x = start[0] + direction[i]
y = start[1] + direction[i+1]
if 0<=x<m and 0<=y<n and (x,y) and board[x][y] == word[idx]:
tmp = board[x][y]
board[x][y] = "*"
if backTracking((x,y),idx+1):
return True
board[x][y] = tmp
return False
for i in range(m):
for j in range(n):
if board[i][j] == word[0]:
tmp = board[i][j]
board[i][j] = "*"
if backTracking((i,j),1):
return True
board[i][j] = tmp
else:
continue
return False
