• Dict & Trie


    208. Implement Trie (Prefix Tree)

    Implement a trie with insertsearch, and startsWith methods.

    Example:

    Trie trie = new Trie();
    
    trie.insert("apple");
    trie.search("apple");   // returns true
    trie.search("app");     // returns false
    trie.startsWith("app"); // returns true
    trie.insert("app");   
    trie.search("app");     // returns true
    class Trie:
    
        def __init__(self):
            """
            Initialize your data structure here.
            """
            self.d = {}
            self.end_of_word = '#'
    
        def insert(self, word: str) -> None:
            """
            Inserts a word into the trie.
            """
            node = self.d
            for char in word:
                node = node.setdefault(char,{})
            node[self.end_of_word] = self.end_of_word
    
        def search(self, word: str) -> bool:
            """
            Returns if the word is in the trie.
            """
            node = self.d
            for char in word:
                if char not in node:
                    return False
                node = node[char]
            return self.end_of_word in node
        
        def startsWith(self, prefix: str) -> bool:
            """
            Returns if there is any word in the trie that starts with the given prefix.
            """
            node = self.d
            for char in prefix:
                if char not in node:
                    return False
                node = node[char]
            return True
    
    
    # Your Trie object will be instantiated and called as such:
    # obj = Trie()
    # obj.insert(word)
    # param_2 = obj.search(word)
    # param_3 = obj.startsWith(prefix)
    实现字典树

    参数运行示范:

    b={};node=b;for char in word:node = node.setdefault(char,{});print(node)

    输出:{}{}{}{}{}

    b  输出:{'a': {'p': {'p': {'l': {'e': {}}}}}}

    node[end_of_word] = end_of_word;node

    输出:{'#': '#'}

    b  输出:{'a': {'p': {'p': {'l': {'e': {'#': '#'}}}}}}

    'a' in node  输出:False

    node = b;'a' in node;  输出:True

    node=node['a'];node;  输出:{'p': {'p': {'l': {'e': {'#': '#'}}}}}

    79. Word Search
    board =
    [
      ['A','B','C','E'],
      ['S','F','C','S'],
      ['A','D','E','E']
    ]
    
    Given word = "ABCCED", return true.
    Given word = "SEE", return true.
    Given word = "ABCB", return false.
    class Solution:
        def exist(self, board: List[List[str]], word: str) -> bool:
            
            if not board:return False
            for i in range(len(board)):
                for j in range(len(board[i])):
                    if self.helper(board,i,j,word):
                        return True
            return False
                        
        
        def helper(self,board,row,col,k):
            if len(k)==0:return True
            if row<0 or row>=len(board) or col<0 or col >=len(board[0]) or k[0]!=board[row][col]:
                return False
            tmp = board[row][col]
            board[row][col]='#'
            res = self.helper(board,row-1,col,k[1:]) or self.helper(board,row+1,col,k[1:]) 
            or self.helper(board,row,col-1,k[1:]) or self.helper(board,row,col+1,k[1:]) 
            board[row][col] = tmp
            return res
    DFS
     
    212. Word Search II
    board = [
      ['o','a','a','n'],
      ['e','t','a','e'],
      ['i','h','k','r'],
      ['i','f','l','v']
    ]
    words = ["oath","pea","eat","rain"]
    
    Output: ["eat","oath"]
    import collections
    dx = [-1,1,0,0]
    dy = [0,0,-1,1]
    END_OF_WORD = '#'
    
    class Solution:
        def findWords(self, board: List[List[str]], words: List[str]) -> List[str]:
            if not board or not board[0]: return []
            if not words: return []
            self.result = set()
            
            root = collections.defaultdict()
            for word in words:
                node = root
                for char in word:
                    node = node.setdefault(char,collections.defaultdict())
                node[END_OF_WORD] = END_OF_WORD
                
            self.m, self.n = len(board),len(board[0])
    
            for i in range(self.m):
                for j in range(self.n):
                    if board[i][j] in root:
                        self._dfs(board,i,j,"",root)
            return list(self.result)
                        
        def _dfs(self,board,i,j,cur_word,cur_dic):
            cur_word+=board[i][j]
            cur_dic = cur_dic[board[i][j]]
            
            if END_OF_WORD in cur_dic:
                self.result.add(cur_word)
                
            tmp,board[i][j] = board[i][j],'@'
            for k in range(4):
                x,y = i + dx[k], j+ dy[k]
                if 0 <= x <self.m and 0<= y < self.n
                    and board[x][y] != '@' and board[x][y] in cur_dic:
                    self._dfs(board,x,y,cur_word,cur_dic)
            board[i][j]=tmp
    字典树+DFS
     
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  • 原文地址:https://www.cnblogs.com/ybxw/p/12918447.html
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