【LeetCode刷题】-- 133.克隆图

133.克隆图

本题就是遍历整个图，遍历的时候要记录已经访问过的节点

方法一：深度优先搜索

/*
// 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 {
    HashMap<Node,Node> visited = new HashMap<>();
    public Node cloneGraph(Node node) {
        if(node == null){
            return node;
        }
        //如果该节点已经被访问过，则直接从哈希表中取出对应的克隆节点返回
        if(visited.containsKey(node)){
            return visited.get(node);
        }
        //克隆节点，注意到为了深拷贝不会克隆他的邻居列表
        Node cloneNode = new Node(node.val,new ArrayList());
        //哈希表存储
        visited.put(node,cloneNode);

        //遍历该节点的邻居并更新克隆节点的邻居列表
        for(Node neighbor : node.neighbors){
            cloneNode.neighbors.add(cloneGraph(neighbor));
        }
        return cloneNode;
        
    }
}

方法二：广度优先搜索

/*
// 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 {
    public Node cloneGraph(Node node) {
        if(node == null){
            return node;
        }
        HashMap<Node,Node> visited = new HashMap<>();
        //将给定的节点添加到队列
        LinkedList<Node> queue = new LinkedList<Node>();
        queue.add(node);
        //克隆第一个节点并存储到哈希表中
        visited.put(node,new Node(node.val,new ArrayList()));

        //广度优先搜索
        while(!queue.isEmpty()){
            //取出队列的头结点
            Node n = queue.remove();
            //遍历该节点的邻居
            for(Node neighbor : n.neighbors){
                if(!visited.containsKey(neighbor)){
                    //如果没有被访问，就克隆并存储到哈希表
                    visited.put(neighbor,new Node(neighbor.val,new ArrayList()));
                    //将邻居节点添加到队列中
                    queue.add(neighbor);
                }
                //更新当前节点的邻居列表
                visited.get(n).neighbors.add(visited.get(neighbor));
            }
        }
        return visited.get(node);
    }
}