LeetCode133.Clone Graph

题目

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

OJ’s undirected graph serialization:
Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.
As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

   1  / \ /   \0 --- 2     / \     \_/

思路

1. 创建一个图副本肯定要遍历原图，可用BFS或DFS

2. 遍历到一个节点A时，我们需要往A的副本A*中添加A的相邻节点B C D的副本B* C* D*

   • 如果A是第一次被遍历，我们可以直接创建其副本
   • 如果A是被多次遍历时，我们需要找到其之前被创建的副本

   因此，我采用一个map<原节点，该节点副本>来记录所有创建出来的节点副本，这样上面第2步操作起来就方便很多了。

代码

/** * Definition for undirected graph. * struct UndirectedGraphNode { *     int label; *     vector<UndirectedGraphNode *> neighbors; *     UndirectedGraphNode(int x) : label(x) {}; * }; */class Solution {public:    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {        unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> nodeMap;        UndirectedGraphNode * clone;        queue<UndirectedGraphNode *> queue;        if(node) {            clone = new UndirectedGraphNode(node->label);            nodeMap[node] = clone;            queue.push(node);        }        else return nullptr;        //采用BFS        while(!queue.empty()) {            UndirectedGraphNode * curr = queue.front();            vector<UndirectedGraphNode *> currNgbs = curr->neighbors;            queue.pop();            for(int i = 0; i < currNgbs.size(); i++) {                //在map找不到该节点，需要创建其副本，并且没有副本说明它之前还没被访问，也需要加进queue继续BFS                if(nodeMap.find(currNgbs[i]) == nodeMap.end()) {                    nodeMap[currNgbs[i]] = new UndirectedGraphNode(currNgbs[i]->label);                    queue.push(currNgbs[i]);                }                (nodeMap[curr]->neighbors).push_back(nodeMap[currNgbs[i]]);            }        }        return clone;    }};