14.1 Clone Graph

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本文提供了一种使用广度优先搜索（BFS）和深度优先搜索（DFS）来解决LeetCode上克隆图问题的方法。通过使用队列和哈希映射，确保每个节点及其邻居被正确复制，避免重复克隆。

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Link: https://oj.leetcode.com/problems/clone-graph/

Approach I: BFS

My first attempt: //Code is not correct.

public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        
        LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        queue.add(node);
        while(!queue.isEmpty()){
            UndirectedGraphNode n = queue.poll();
            UndirectedGraphNode newNode = new UndirectedGraphNode(n.label);
            ArrayList<UndirectedGraphNode> list = new ArrayList<UndirectedGraphNode>();
            for(UndirectedGraphNode neighbor : n.neighbors){
                list.add(neighbor);
                queue.add(neigbhor);
            }
            newNode.neighbors = new ArrayList<UndirectedGraphNode>(list);
        }
        return newNode;
    }
}

Correct Answer:

public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if(node == null) return null;
        LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
        map.put(node, copy);
        queue.add(node);
        
        while(!queue.isEmpty()){
            UndirectedGraphNode cur = queue.poll();
            for(int i = 0; i < cur.neighbors.size(); i++){
                UndirectedGraphNode neighbor = cur.neighbors.get(i);
                if(!map.containsKey(neighbor)){
                    copy = new UndirectedGraphNode(neighbor.label);
                    map.put(neighbor, copy);
                    queue.add(neighbor);
                }
                map.get(cur).neighbors.add(map.get(neighbor));//map.get(cur) is the copy of cur
            }
        }
        return map.get(node);
    }
}

Approach II: DFS

Just replace queue by stack???