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Problem solution · Python

Accounts Merge

Accounts Merge: a Python solution using disjoint set union. Learn the idea, check the complexity, and read the full code, with credit to Kamyu LeetCode Solutions.

Technique
Disjoint set union
Source
Kamyu LeetCode Solutions
Length
53 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Disjoint set union

For Accounts Merge, the implementation maintains connected components and merges them as relationships are processed.

  1. Give each element a component representative.
  2. Merge representatives when a connection is accepted.
  3. Answer connectivity or component queries from the compressed representatives.

Code notes

  • 53 lines of Python from the credited upstream file accounts-merge.py.
  • The implementation visibly relies on sequence storage, hash lookup, ordered lookup.
  • No explicit loop blocks detected.

Complexity

Account for every find and union operation; with path compression and ranked merging, the amortized cost is nearly constant per operation.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from Kamyu LeetCode Solutions by kamyu104 and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeAccounts Merge · PythonPython
Use this to learn the idea, then write your own version.
# Time:  O(nlogn), n is the number of total emails,#                  and the max length ofemail is 320, p.s. {64}@{255}# Space: O(n) import collections  class UnionFind(object):    def __init__(self):        self.set = []     def get_id(self):        self.set.append(len(self.set))        return len(self.set)-1     def find_set(self, x):        if self.set[x] != x:            self.set[x] = self.find_set(self.set[x])  # path compression.        return self.set[x]     def union_set(self, x, y):        x_root, y_root = map(self.find_set, (x, y))        if x_root != y_root:            self.set[min(x_root, y_root)] = max(x_root, y_root)  class Solution(object):    def accountsMerge(self, accounts):        """        :type accounts: List[List[str]]        :rtype: List[List[str]]        """        union_find = UnionFind()        email_to_name = {}        email_to_id = {}        for account in accounts:            name = account[0]            for i in xrange(1, len(account)):                if account[i] not in email_to_id:                    email_to_name[account[i]] = name                    email_to_id[account[i]] = union_find.get_id()                union_find.union_set(email_to_id[account[1]],                                     email_to_id[account[i]])         result = collections.defaultdict(list)        for email in email_to_name.keys():            result[union_find.find_set(email_to_id[email])].append(email)        for emails in result.values():            emails.sort()        return [[email_to_name[emails[0]]] + emails                for emails in result.values()]

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