Create 16. Alien Dictionary.py

07_Graph/16. Alien Dictionary.py

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+# https://www.geeksforgeeks.org/problems/alien-dictionary/1
+# https://www.youtube.com/watch?v=6kTZYvNNyps
+
+class Solution:
+    def findOrder(self,alien_dict, N, K):
+
+        adj = {char: set() for word in alien_dict for char in word}
+
+        for i in range(len(alien_dict) - 1):
+            w1, w2 = alien_dict[i], alien_dict[i + 1]
+            minLen = min(len(w1), len(w2))
+            if len(w1) > len(w2) and w1[:minLen] == w2[:minLen]:
+                return ""
+            for j in range(minLen):
+                if w1[j] != w2[j]:
+                    adj[w1[j]].add(w2[j])
+                    break
+
+        visited = {}  # {char: bool} False visited, True current path
+        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 "".join(res)
+
+