Redundant Connection

Asked byGoogleMicrosoft

Problem

A graph started as a tree with n nodes and had exactly one extra edge added, creating a single cycle. Given the edges, find the edge that can be removed so the graph becomes a tree again; if more than one edge could be removed, return the one that appears last in the input.

Examples

Example 1

Input:edges = [[1,2],[1,3],[2,3]]

Output:[2,3]

Constraints

n == edges.length
3 <= n <= 1000

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How to approach it: the Graphs pattern

A graph models relationships as nodes and edges, which can be directed or undirected, weighted or not. Most graph problems come down to choosing the right traversal — DFS, BFS, or union-find — for what you're trying to find.

Look for this pattern when

The problem involves connections between items (islands, courses with prerequisites, friend networks, grids).
You need the shortest path in an unweighted graph (BFS) or need to explore every reachable node (DFS).
You're asking "are these two things connected?" repeatedly (union-find).

Read the full Graphs guide →

Video walkthroughs

Original problem on LeetCode ↗