算法练习笔记（五）— 图

汇编真是世界上最可怕的语言之一

不想说话

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题目地址：https://leetcode.com/problems/clone-graph/#/description

题目：Clone Graph

描述：

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         / \         \_/

关于图的邻接表链表表示的定义题，题目最大的问题在于没有明确解答的目的

导致很多人（包括我）绕了很大个圈子才绕过来

解答：

/** * Definition for undirected graph. * struct UndirectedGraphNode { *     int label; *     vector<UndirectedGraphNode *> neighbors; *     UndirectedGraphNode(int x) : label(x) {}; * }; */class Solution {public:    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {       if(node == NULL)return NULL;       if(mymap.find(node) == mymap.end()){                                //mymap.find(node) == mymap.end();           mymap[node] = new UndirectedGraphNode(node -> label);           for(UndirectedGraphNode * h : node -> neighbors){               mymap[node] -> neighbors.push_back(cloneGraph(h));   //遍历           }       }       return mymap[node];    }private:    map<UndirectedGraphNode *, UndirectedGraphNode *> mymap;};