LC-0684 Medium LeetCode

684. Redundant Connection

Depth-First Search Breadth-First Search Union Find Graph

Read the full problem statement on LeetCode.

Difficulty: medium Acceptance: 66% Topics: Depth-First Search, Breadth-First Search, Union Find, Graph

Reading material

Trees & Traversals 18 min Union–Find (DSU) 12 min Graphs 16 min

Reference solution (spoiler · python)

# Time:  O(nlog*n) ~= O(n), n is the length of the positions
# Space: O(n)

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 findRedundantConnection(self, edges):
        """
        :type edges: List[List[int]]
        :rtype: List[int]
        """
        union_find = UnionFind(len(edges)+1)
        for edge in edges:
            if not union_find.union_set(*edge):
                return edge
        return []

Solution from kamyu104/LeetCode-Solutions · MIT