S212-搜索+字典树-212. Word Search II-（Hard）

一、题目

　　

　　　题目很简单，输入一个字母组成的二维数组，以某一个字母为起点，向、上下左右搜索、练成的字符看是不是在给定的字符串数组中

二、解答

　　通过深度优先搜索，每一步和数组中的字符串匹配是可以计算出来正确结果的，但是结果超时

　　重点是匹配的过程时间太长

　　通过字典树，可以优化两点

　　一是检索某个字符串在不在的时间

　　一是一个某个字符串前缀的字符串是否存在于字符串数组中

　　最终的答案：

　　注意，结果去重

class Trie:
	def __init__(self):
		"""
		Initialize your data structure here.
		"""
		self.x = {}
		self.p = {}

	def insert(self, word):
		"""
		Inserts a word into the trie.
		:type word: str
		:rtype: void
		"""
		if word:
			self.x[word] = True
			for i in range(1,len(word)+1):
				self.p[word[0:i]] = True

	def search(self, word):
		"""
		Returns if the word is in the trie.
		:type word: str
		:rtype: bool
		"""

		for x in self.x:
			if word == x:
				return True
		return False

	def startsWith(self, prefix):
		"""
		Returns if there is any word in the trie that starts with the given prefix.
		:type prefix: str
		:rtype: bool
		"""
		return prefix in self.p

class Solution:
	def findWords(self, board, words):
		"""
		:type board: List[List[str]]
		:type words: List[str]
		:rtype: List[str]
		"""
		t = Trie()
		for word in words:
			t.insert(word)

		visited = [([0 for j in range(len(board[0]))]) for i in range(len(board))]
		res = []
		for row in range(len(board)):
			for col in range(len(board[0])):
				self.DFS(board, visited, "", row, col, t, res)

		return list(set(res))

	def DFS(self, board, visited, temp_str, pos_row, pos_col, t, res):
		if pos_row < 0 or pos_row >= len(board) or pos_col < 0 or pos_col >= len(board[0]):
			return
#		print(pos_row, pos_col, visited)
		if visited[pos_row][pos_col] == 1:
			return
		temp_str += board[pos_row][pos_col]
		if not t.startsWith(temp_str):
			return
		if t.search(temp_str):
			res.append(temp_str)

		visited[pos_row][pos_col] = 1
		self.DFS(board, visited, temp_str, pos_row, pos_col + 1, t, res)
		self.DFS(board, visited, temp_str, pos_row - 1, pos_col, t, res)
		self.DFS(board, visited, temp_str, pos_row, pos_col - 1, t, res)
		self.DFS(board, visited, temp_str, pos_row + 1, pos_col, t, res)
		visited[pos_row][pos_col] = 0

if __name__ == "__main__":
	s = Solution()
#	print(s.findWords([
#			['o','a','a','n'],
#			['e','t','a','e'],
#			['i','h','k','r'],
#			['i','f','l','v']
#		],
#		["oath","pea","eat","rain"]))

	print(s.findWords([["b"],["a"],["b"],["b"],["a"]],
						["baa","abba","baab","aba"]))

　　

三、参考

　　https://blog.csdn.net/ljiabin/article/details/45846527