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| 1 | +#!/usr/bin/python3 |
| 2 | +""" |
| 3 | +Given a 2D board and a list of words from the dictionary, find all words in the board. |
| 4 | +
|
| 5 | +Each word must be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally |
| 6 | +or vertically neighboring. The same letter cell may not be used more than once in a word. |
| 7 | +
|
| 8 | +For example, |
| 9 | +Given words = ["oath","pea","eat","rain"] and board = |
| 10 | +
|
| 11 | +[ |
| 12 | + ['o','a','a','n'], |
| 13 | + ['e','t','a','e'], |
| 14 | + ['i','h','k','r'], |
| 15 | + ['i','f','l','v'] |
| 16 | +] |
| 17 | +Return ["eat","oath"]. |
| 18 | +Note: |
| 19 | +You may assume that all inputs are consist of lowercase letters a-z. |
| 20 | +""" |
| 21 | +from typing import List |
| 22 | +from collections import defaultdict |
| 23 | + |
| 24 | + |
| 25 | +dirs = [(0, 1), (0, -1), (-1, 0), (1, 0)] |
| 26 | + |
| 27 | + |
| 28 | +class TrieNode: |
| 29 | + def __init__(self): |
| 30 | + self.word = None |
| 31 | + self.children = defaultdict(TrieNode) |
| 32 | + |
| 33 | + |
| 34 | +class Solution: |
| 35 | + def findWords(self, board: List[List[str]], words: List[str]) -> List[str]: |
| 36 | + root = self.construct(words) |
| 37 | + m, n = len(board), len(board[0]) |
| 38 | + visited = [[False for _ in range(n)] for _ in range(m)] |
| 39 | + ret = set() |
| 40 | + for i in range(m): |
| 41 | + for j in range(n): |
| 42 | + self.dfs(board, visited, i, j, root, ret) |
| 43 | + |
| 44 | + return list(ret) |
| 45 | + |
| 46 | + def dfs(self, board, visited, i, j, cur, ret): |
| 47 | + m, n = len(board), len(board[0]) |
| 48 | + visited[i][j] = True |
| 49 | + c = board[i][j] |
| 50 | + if c in cur.children: |
| 51 | + nxt = cur.children[c] |
| 52 | + if nxt.word is not None: |
| 53 | + ret.add(nxt.word) |
| 54 | + |
| 55 | + for di, dj in dirs: |
| 56 | + I = i + di |
| 57 | + J = j + dj |
| 58 | + if 0 <= I < m and 0 <= J < n and not visited[I][J]: |
| 59 | + self.dfs(board, visited, I, J, nxt, ret) |
| 60 | + |
| 61 | + visited[i][j] = False |
| 62 | + |
| 63 | + def construct(self, words): |
| 64 | + root = TrieNode() |
| 65 | + for w in words: |
| 66 | + cur = root |
| 67 | + for c in w: |
| 68 | + cur = cur.children[c] |
| 69 | + cur.word = w |
| 70 | + |
| 71 | + return root |
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