Given an m x n grid of characters board and a string word, return true if word exists in the grid.
The word can be constructed from letters of sequentially adjacent cells, where adjacent cells are horizontally or vertically neighboring. The same letter cell may not be used more than once.
Example 1:
Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCCED"
Output: true
Example 2:
Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "SEE"
Output: true
Example 3:
Input: board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCB"
Output: false
Solution
class Solution:
def exist(self, board: List[List[str]], word: str) -> bool:
rows = len(board)
cols = len(board[0])
path = set()
def dfs(r, c, i):
if i == len(word):
return True
if r < 0 or c < 0 or r >= rows or c >= cols or word[i] != board[r][c] or (r,c) in path:
return False
path.add((r, c))
out = dfs(r + 1, c, i + 1) or dfs(r - 1, c, i + 1) or dfs(r, c + 1, i + 1) or dfs(r, c - 1, i + 1)
path.remove((r, c))
return out
for r in range(rows):
for c in range(cols):
if dfs(r, c, 0): return True
return False