LeetCode in Net

133. Clone Graph

Medium

Given a reference of a node in a connected undirected graph.

Return a deep copy (clone) of the graph.

Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors.

class Node { public int val; public List neighbors; }

Test case format:

For simplicity, each node’s value is the same as the node’s index (1-indexed). For example, the first node with val == 1, the second node with val == 2, and so on. The graph is represented in the test case using an adjacency list.

An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph.

The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph.

Example 1:

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

Output: [[2,4],[1,3],[2,4],[1,3]]

Explanation:

There are 4 nodes in the graph.
1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). 

Example 2:

Input: adjList = [[]]

Output: [[]]

Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors.

Example 3:

Input: adjList = []

Output: []

Explanation: This an empty graph, it does not have any nodes.

Example 4:

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

Output: [[2],[1]]

Constraints:

• The number of nodes in the graph is in the range [0, 100].
• 1 <= Node.val <= 100
• Node.val is unique for each node.
• There are no repeated edges and no self-loops in the graph.
• The Graph is connected and all nodes can be visited starting from the given node.

Solution

public class Node {
    public int val;
    public IList<Node> neighbors;

    public Node() {
        val = 0;
        neighbors = new List<Node>();
    }

    public Node(int _val) {
        val = _val;
        neighbors = new List<Node>();
    }

    public Node(int _val, List<Node> _neighbors) {
        val = _val;
        neighbors = _neighbors;
    }

    public override string ToString() {
        var result = new System.Text.StringBuilder();
        result.Append('[');
        bool first = true;
        foreach (var node in neighbors) {
            if (!first) {
                result.Append(',');
            }
            if (node.neighbors == null || node.neighbors.Count == 0) {
                result.Append(node.val);
            } else {
                var inner = new System.Text.StringBuilder();
                inner.Append('[');
                bool innerFirst = true;
                foreach (var nodeItem in node.neighbors) {
                    if (!innerFirst) {
                        inner.Append(',');
                    }
                    inner.Append(nodeItem.val);
                    innerFirst = false;
                }
                inner.Append(']');
                result.Append(inner.ToString());
            }
            first = false;
        }
        result.Append(']');
        return result.ToString();
    }
}

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