Clone Graph

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Problem

Given a reference to a node in a connected undirected graph, return a deep copy (clone) of the graph, where each node holds a value and a list of references to its neighbors.

Examples

Example 1

Input:adjList = [[2,4],[1,3],[2,4],[1,3]]

Output:a cloned graph with the same adjacency structure

Constraints

The number of nodes is in the range [0, 100].

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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 ↗