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

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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