Solve : Alien Dictionary

Author: printjin-gmailcom

alien-dictionary/printjin-gmailcom.py

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+import collections
+class Solution:
+    def alien_order(self, words):
+        graph = collections.defaultdict(set)
+        indegree = {}
+        for word in words:
+            for c in word:
+                indegree[c] = 0
+        for i in range(len(words) - 1):
+            w1, w2 = words[i], words[i + 1]
+            min_len = min(len(w1), len(w2))
+            if len(w1) > len(w2) and w1[:min_len] == w2[:min_len]:
+                return "" 
+            for j in range(min_len):
+                if w1[j] != w2[j]:
+                    if w2[j] not in graph[w1[j]]:
+                        graph[w1[j]].add(w2[j])
+                        indegree[w2[j]] += 1
+                    break
+        queue = collections.deque([c for c in indegree if indegree[c] == 0])
+        res = []
+        while queue:
+            c = queue.popleft()
+            res.append(c)
+            for nei in graph[c]:
+                indegree[nei] -= 1
+                if indegree[nei] == 0:
+                    queue.append(nei)
+        return "".join(res) if len(res) == len(indegree) else ""