Clone Graph -- leetcode - c++编程基础

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 #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.

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:

给出一个无向连通图，要求复制

基本思路：

对图的遍历，采取广度优先或者深度优先。

遍历时，需要记住已访问的结点。避免重复访问。这功能可以和下面的map重用。

另外需要一个map，映射，当前节点，和其对应的复制节点。

访问每一个节点时，需要复制其邻接边。对题目来讲，就是复制其 neighbours数组。

当边所引用的节点不存在时，需要创建此结点。

以下深度优先实现方式。在leetcode上实际执行时间为 72ms。

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector
    
      neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (!node) return node;
        stack
     
       s; unordered_map
      
        m; s.push(node); auto root = new UndirectedGraphNode(node->label); m[node] = root; while (!s.empty()) { node = s.top(); s.pop(); auto node_copy = m[node]; for (auto neighbor: node->neighbors) { auto ? = m[neighbor]; if (!copy) { s.push(neighbor); copy = new UndirectedGraphNode(neighbor->label); } node_copy->neighbors.push_back(copy); } } return root; } };

广度优先实际方式。在leetcode上执行时间为76ms。

即将上面算法的stack换成了queue。

class Solution {
public:
    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (!node) return node;
        queue
    
      q;
        unordered_map
     
       m; q.push(node); auto root_copy = new UndirectedGraphNode(node->label); m[node] = root_copy; while (!q.empty()) { node = q.front(); q.pop(); auto node_copy = m[node]; for (auto neighbor: node->neighbors) { auto ? = m[neighbor]; if (!copy) { q.push(neighbor); copy = new UndirectedGraphNode(neighbor->label); } node_copy->neighbors.push_back(copy); } } return root_copy; } };