0133. Clone Graph (M)

Clone Graph (M)

题目

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 val (int) and a list (List[Node]) of its neighbors.

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

Test case format:

For simplicity sake, 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.

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:

• 1 <= Node.val <= 100
• Node.val is unique for each node.
• Number of Nodes will not exceed 100.
• There is 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.

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题意

复制一个图。

思路

深拷贝一个图，递归处理即可。一个结点的标识符是它的val值，每次复制一个结点，将它存入map中，当下一次再遇到这个结点时，直接返回已经map中存储的已经复制的。

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代码实现

Java

class Solution {
    private Map<Integer, Node> cloned = new HashMap<>();

    public Node cloneGraph(Node node) {
        if (node == null) {
            return null;
        }
      
        if (cloned.containsKey(node.val)) {
            return cloned.get(node.val);
        }
      
        Node clone = new Node(node.val);
        cloned.put(node.val, clone);	   // 注意一定要先保存到map再进行递归
        for (Node tmp : node.neighbors) {
            clone.neighbors.add(cloneGraph(tmp));
        }
        return clone;
    }
}