Word Squares — LeetCode 425 Python Solution

class Trie:
    def __init__(self):
        self.children = [None] * 26
        self.v = []

    def insert(self, w, i):
        node = self
        for c in w:
            idx = ord(c) - ord('a')
            if node.children[idx] is None:
                node.children[idx] = Trie()
            node = node.children[idx]
            node.v.append(i)

    def search(self, w):
        node = self
        for c in w:
            idx = ord(c) - ord('a')
            if node.children[idx] is None:
                return []
            node = node.children[idx]
        return node.v


class Solution:
    def wordSquares(self, words: List[str]) -> List[List[str]]:
        def dfs(t):
            if len(t) == len(words[0]):
                ans.append(t[:])
                return
            idx = len(t)
            pref = [v[idx] for v in t]
            indexes = trie.search(''.join(pref))
            for i in indexes:
                t.append(words[i])
                dfs(t)
                t.pop()

        trie = Trie()
        ans = []
        for i, w in enumerate(words):
            trie.insert(w, i)
        for w in words:
            dfs([w])
        return ans