LeetCode 19 Clone Graph

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

分析：

广度优先遍历，涉及队列的应用，

节点有没有访问过的标记，HashMap的应用。

/** * Definition for undirected graph. * class UndirectedGraphNode { *     int label; *     List<UndirectedGraphNode> neighbors; *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } * }; */public class Solution {    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {        if(node == null) return null;        //广度优先遍历的常规技术，利用队列        Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();        //HashMap用来标记节点有没有访问过        HashMap<UndirectedGraphNode,UndirectedGraphNode> hashMap = new HashMap<UndirectedGraphNode,UndirectedGraphNode>();        //先把第一个节点放进队列，完成初始化        queue.add(node);        UndirectedGraphNode clone = new UndirectedGraphNode(node.label);        hashMap.put(node, clone);        //开始遍历        while(!queue.isEmpty()){            UndirectedGraphNode curr = queue.remove();            UndirectedGraphNode currClone = hashMap.get(curr);            //对于当前节点的邻居            for(UndirectedGraphNode item : curr.neighbors){                //如果在hashMap里，说明已经访问过，建立指针关系即可                if(hashMap.containsKey(item)){                    currClone.neighbors.add(hashMap.get(item));                }else{//如果没有在hashMap里，说明没有访问过，除了新建节点并建立指针关系外，                    //还要再hashMap里放入新对，并将没有访问过的节点入队                    UndirectedGraphNode newItem = new UndirectedGraphNode(item.label);                    currClone.neighbors.add(newItem);                    hashMap.put(item, newItem);                    queue.add(item);                }            }        }        return clone;    }}