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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.
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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:
1
/ \
/ \
0 --- 2
/ \
\_/
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给出一个无向连通图，要求复制
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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。
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以下深度优先实现方式。在leetcode上实际执行时间为 72ms。
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/**
* 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。
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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; } };
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