Alien Dictionary

#User function Template for python3

class Solution:
    def findOrder(self,alien_dict, N, K):
        adj = {chr(97+idx): set() for idx in range(K)}

        for i in range(N - 1):
            word_one, word_two = alien_dict[i], alien_dict[i + 1]
            length = min(len(word_one), len(word_two))
            for j in range(length):
                if word_one[j] != word_two[j]:
                    adj[word_one[j]].add(word_two[j])
                    break

        visited = {}
        res = []

        def dfs(char):
            if char in visited:
                return visited[char]

            visited[char] = True

            for neighChar in adj[char]:
                if dfs(neighChar):
                    return True

            visited[char] = False
            res.append(char)

        for char in adj:
            if dfs(char):
                return []
        res.reverse()
        return res