LC-0924 Hard LeetCode

924. Minimize Malware Spread

Array Hash Table Depth-First Search Breadth-First Search Union Find Graph

Read the full problem statement on LeetCode.

Difficulty: hard Acceptance: 42% Topics: Array, Hash Table, Depth-First Search, Breadth-First Search, Union Find, Graph

Reading material

Arrays & Hashing 12 min Trees & Traversals 18 min Union–Find (DSU) 12 min

Reference solution (spoiler · python)

# Time:  O(n^2)
# Space: O(n)

import collections


class UnionFind(object):
    def __init__(self, n):
        self.set = range(n)

    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:
            return False
        self.set[min(x_root, y_root)] = max(x_root, y_root)
        return True


class Solution(object):
    def minMalwareSpread(self, graph, initial):
        """
        :type graph: List[List[int]]
        :type initial: List[int]
        :rtype: int
        """
        union_find = UnionFind(len(graph))
        for i in xrange(len(graph)):
            for j in xrange(i+1, len(graph)):
                if graph[i][j] == 1:
                    union_find.union_set(i, j)
        union_size = collections.Counter(union_find.find_set(i) for i in xrange(len(graph)))
        malware_count = collections.Counter(union_find.find_set(i) for i in initial)
        return min(initial, key=lambda x: [malware_count[union_find.find_set(x)] > 1,
                                           -union_size[union_find.find_set(x)],
                                           x])

Solution from kamyu104/LeetCode-Solutions · MIT