Please design a function to judge whether there is a path containing all characters of a certain string in a matrix. The path can start from any grid in the matrix, and each step can move one grid to the left, right, up and down in the matrix. If a path passes through a grid of the matrix, the path cannot enter the grid again. For example, the following 3 × 4 matrix contains a path of the character string “bfce” (the letters in the path are marked in bold).
[["a","b","c","e"],
["s","f","c","s"],
["a","d","e","e"]]
But the matrix does not contain the path of the string "abfb" because the first character b of the string occupies the second grid in the first row of the matrix, the path cannot enter this grid again.
Example 1:
输入：board = [["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], word = "ABCCED"
输出：true
Example 2:
输入：board = [["a","b"],["c","d"]], word = "abcd"
输出：false
prompt:
1 <= board.length <= 200
1 <= board [i] .length <= 200
Note: This question is the same as the main station 79 question: https://leetcode-cn.com/problems/word-search/
Source: LeetCode (LeetCode)
link: https://leetcode-cn.com/problems/ju-zhen-zhong-de-lu-jing-lcof
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Idea: Deep Search (dfs)
First traverse the array, try each point as a starting point, and then start searching from all directions of the starting point to see if a path can be found.
class Solution:
def exist(self, board: List[List[str]], word: str) -> bool:
if board == [] or board == [[]]:
return False
# 标记该点是否在本次路径中搜索过
self.visit = [[0]*len(board[0]) for _ in range(len(board))]
# 每个点的周边点，分别为x,y的变化值
self.dx = [0, 0, 0, 1, -1]
self.dy = [0, 1, -1, 0, 0]
self.board = board
self.word = word
for i in range(len(board)):
for j in range(len(board[0])):
rt = self.dfs(i, j, 0)
if rt == True:
return True
return False
def dfs(self, x, y, cnt):
if cnt == len(self.word):
return True
for i in range(len(self.dx)):
xx = x + self.dx[i]
yy = y + self.dy[i]
if xx >= 0 and xx < len(self.board) and yy >= 0 and yy < len(self.board[0]) and self.visit[xx][yy] == 0:
if self.board[xx][yy] == self.word[cnt]:
self.visit[xx][yy] = 1
# print(xx, yy)
rt = self.dfs(xx, yy, cnt+1)
if rt == True:
return True
self.visit[xx][yy] = 0
return False
