721

Author: ProHiryu

DFS/traditionalDFS/721.md

@@ -0,0 +1,53 @@
+## Accounts Merge
+
+#### Description
+
+[link](https://leetcode.com/problems/accounts-merge/description/)
+
+---
+
+#### Solution
+
+- See Code
+
+此题最巧妙之处在于使用邮箱并查集方式查找对应的账号，通过这种方式把所有连通的账号遍历完成，在DFS的过程中记录答案emails
+
+---
+
+#### Code
+
+> 最坏情况：O(n^2)
+
+```python
+class Solution:
+    def accountsMerge(self, accounts: List[List[str]]) -> List[List[str]]:
+        from collections import defaultdict
+        visited_accounts = [False] * len(accounts)
+        emails_accounts_map = defaultdict(list)
+        res = []
+        # Build up the graph.
+        for i, account in enumerate(accounts):
+            for j in range(1, len(account)):
+                email = account[j]
+                emails_accounts_map[email].append(i)
+
+        # DFS code for traversing accounts.
+        def dfs(i, emails):
+            if visited_accounts[i]:
+                return
+            visited_accounts[i] = True
+            for j in range(1, len(accounts[i])):
+                email = accounts[i][j]
+                emails.add(email)
+                for neighbor in emails_accounts_map[email]:
+                    dfs(neighbor, emails)
+
+        # Perform DFS for accounts and add to results.
+        for i, account in enumerate(accounts):
+            if visited_accounts[i]:
+                continue
+            name, emails = account[0], set()
+            dfs(i, emails)
+            res.append([name] + sorted(emails))
+        return res
+```