Leetcode133. 克隆图

题目传送： ​​https://leetcode.cn/problems/clone-graph/​​

运行效率：

代码如下：

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> neighbors;
    public Node() {
        val = 0;
        neighbors = new ArrayList<Node>();
    }
    public Node(int _val) {
        val = _val;
        neighbors = new ArrayList<Node>();
    }
    public Node(int _val, ArrayList<Node> _neighbors) {
        val = _val;
        neighbors = _neighbors;
    }
}
*/

class Solution {
    //用于记录哪些结点已经被克隆过
 HashMap<Node, Node> visited = new HashMap<>();
 public Node cloneGraph(Node node) {
    // 处理边界情况
    if (node == null) {
      return null;
    }
    //如果该节点已经被克隆过，那就直接返回该节点的克隆节点
    if(visited.containsKey(node)){
      return visited.get(node);
    }
    ArrayList<Node> neighbors = new ArrayList();
    // 克隆当前的节点
    Node cloneNode = new Node(node.val, neighbors);
    // 添加到visited中,  意味着当前节点已经被克隆完毕
    visited.put(node, cloneNode);
    // 接着要克隆当前节点的邻居节点
    for (Node neighbor : node.neighbors) {
      Node cloneNeighbor = cloneGraph(neighbor);
      neighbors.add(cloneNeighbor);
    }
    return visited.get(node);//返回克隆的结点
  }
}