208. Implement Trie (Prefix Tree)
Implement a trie with insert
, search
, 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)
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
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