LC-0721 Medium LeetCode

721. Accounts Merge

Array Hash Table String Depth-First Search Breadth-First Search Union Find Sorting

Read the full problem statement on LeetCode.

Difficulty: medium Acceptance: 59% Topics: Array, Hash Table, String, Depth-First Search, Breadth-First Search, Union Find, Sorting

View full problem on LeetCode

Reading material

Arrays & Hashing 12 min Strings 12 min Trees & Traversals 18 min

Reference solution (spoiler · python)

# 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()]

Solution from kamyu104/LeetCode-Solutions · MIT